System and method for determining data rate

ABSTRACT

Described herein are systems and methods for determining data rate in a direct sequence spread spectrum system. The systems may include circuits or processors for receiving a signal that was transmitted at an unknown data rate and determining the value of the unknown data rate based on a sequence of bits that is generated from processing the signal according to a first data rate. The methods may include receiving a signal having an unknown data rate, processing the signal according to a first data rate, generating another signal that corresponds to a sequence of bits that result from the processing, and determining the value of the unknown data rate according to the sequence of bits.

CROSS-REFERENCE TO RELATED APPLICATIONS Claiming Benefit Under 35 U.S.C.120

This application is a continuation of U.S. application Ser. No.09/723,930 filed Nov. 28, 2000; which is a divisional of applicationSer. No. 09/129,448, filed Aug. 4, 1998, now U.S. Pat. No. 6,970,434,issued Nov. 29, 2005; which is a continuation of U.S. application Ser.No. 08/487,609 filed Jun. 7, 1995, now U.S. Pat. No. 5,790,536 issuedAug. 4, 1998; which is a continuation-in-part of U.S. application Ser.Nos. 08/279,148, filed Jul. 22, 1994, now U.S. Pat. No. 5,657,317; whichis a continuation-in-part of U.S. application Ser. No. 08/198,404, filedFeb. 22, 1994 abandoned; which is a continuation of U.S. applicationSer. No. 08/198,452, filed Feb. 18, 1994, abandoned; which is acontinuation-in-part of U.S. application Ser. No. 08/168,478, filed Dec.16, 1993, abandoned; which is a continuation-in-part of U.S. applicationSer. No. 08/147,377 filed Nov. 3, 1993, abandoned; which is acontinuation-in-part of U.S. application Ser. No. 08/101,254, filed Aug.3, 1993 now abandoned; which is a continuation-in-part of U.S.application Ser. No. 08/085,662, filed Jun. 29, 1993 now abandoned whichis a continuation-in-part of U.S. application Ser. No. 08/076,340, filedJun. 11, 1993 now abandoned which is a continuation-in-part of U.S.application Ser. No. 08/062,457, filed May 11, 1993 now abandoned.

PCT Application Serial No. PCT/US93/12628 is based on U.S. applicationSer. No. 08/027,140 filed Mar. 5, 1993, which is itself acontinuation-in-part of U.S. application Ser. No. 07/997,693 filed Dec.23, 1992, now abandoned, which is a continuation-in-part of U.S.application Ser. No. 07/982,292 filed Nov. 27, 1992, now abandoned,which is itself a continuation-in-part of U.S. application Ser. No.07/700,704 filed May 14, 1991, now abandoned, which is itself acontinuation-in-part of U.S. application Ser. No. 07/699,818 filed May13, 1991, now abandoned.

The application U.S. Ser. No. 08/205,639 is a continuation-in-part ofU.S. application Ser. No. 07/735,128 filed Jul. 22, 1991, which isitself a continuation-in-part of U.S. application Ser. No. 07/467,096filed Jan. 18, 1990, now U.S. Pat. No. 5,052,020.

U.S. application Ser. No. 08/062,457 is a continuation in part of U.S.Ser. No. 07/876,776, filed Apr. 28, 1992, which is itself a continuationin part of U.S. Ser. No. 07/854,115, filed Mar. 18, 1992, which is inturn a continuation in part of U.S. Ser. No. 07/558,895, filed Jul. 25,1990. U.S. Ser. No. 07/558,895 is a continuation in part of U.S. Ser.No. 07/529,353, filed May 25, 1990, which is itself a continuation inpart of U.S. Ser. No. 07/347,602, filed May 3, 1989, which is itself acontinuation of U.S. Ser. No. 07/345,771, filed May 2, 1989, which isitself a continuation of U.S. Ser. No. 07/345,200, filed Apr. 28, 1989,which is itself a continuation of U.S. Ser. No. 07/305,302, filed Jan.31, 1989.

The application U.S. Ser. No. 07/876,629 is also a continuation in partof U.S. Ser. No. 07/854,115, filed Mar. 18, 1992, with its parentage aslisted above.

The application U.S. Ser. No. 08/267,758 is a continuation in part ofU.S. Ser. No. 07/748,150, filed Aug. 21, 1991, now issued as U.S. Pat.No. 5,349,678 on Sep. 20, 1994.

INCORPORATION BY REFERENCE

The above referenced applications, PCT Application No. PCT/US92/08610filed Oct. 1, 1992, as published under International Publication No. WO93/07691 on Apr. 15, 1993, together with U.S. Pat. No. 5,070,536, byMahany et al., U.S. Pat. No. 4,924,426, by Sojka, and U.S. Pat. No.4,910,794, by Mahany, are incorporated herein by reference In theirentirety, including drawings and appendices, and hereby are made a partof this application.

Also incorporated herein by reference in their entirety, includingdrawings and appendices, are Mahany U.S. Pat. No. 5,696,903 issued Dec.9, 1997, and Mahany, et al., U.S. Pat. No. 5,657,317 issued Aug. 12,1997, and U.S. Pat. No. 5,790,536 issued Aug. 4, 1998.

TECHNICAL FIELD

The present invention relates generally to communication networks havinga plurality of wired and/or wireless access servers configured toprovide remote processing and data storage. More specifically, thisinvention relates to the intelligent migration of programs and datathrough a wireless and hardwired communication network comprised of aplurality of access servers, computers and peripherals.

BACKGROUND OF THE INVENTION

Multiple radio base station networks have been developed to overcome avariety of problems with single radio base station networks such asspanning physical radio wave penetration barriers, wasted transmissionpower by portable computing devices, etc. However, multiple radio basestation networks have their own inherent problems. For example, in amultiple base station network employing a single shared channel, eachbase station transmission is prone to collision with neighboring basestation transmissions in the overlapping coverage areas between the basestations. Therefore, it often proves undesirable for each base stationto use a single or common communication channel.

In contradistinction, to facilitate the roaming of portable or mobiledevices from one coverage area to another, use of a common communicationchannel for all of the base stations is convenient. A roaming device mayeasily move between coverage areas without loss of connectivity to thenetwork.

Such exemplary competing commonality factors have resulted in tradeoffdecisions in network design. These factors become even more significantwhen implementing a frequency hopping spread spectrum network. Frequencyhopping is a desirable transmission technique because of its ability tocombat frequency selective fading, avoid narrowband interference, andprovide multiple communications channels.

Again, however, changing operating parameters between coverage areascreates difficulties for the roaming devices which move therebetween. Inparticular, when different communication parameters are used, a portableor mobile device roaming into a new base station coverage area is notable to communicate with the new base station without obtaining andsynchronizing to the new parameters. This causes communication backlogin the network.

Computer terminals and peripheral devices are widely used. Many types ofcomputer terminals exist which vary greatly in terms of function, powerand speed. Many different types of peripheral devices also exist, suchas printers, modems, graphics scanners, text scanners, code readers,magnetic card readers, external monitors, voice command interfaces,external storage devices, and so on.

To communicate with such peripheral devices, portable computers havebeen adapted to use RF (Radio Frequency) and infrared communication.Such configurations, however, do not always provide for efficientcommunication. For example, a portable computer device may be mounted ina delivery truck and a driver may desire to transmit data to, or receivedata from, a host computer or peripheral device at a remote warehouselocation. While permitting such transmissions, wide area networks (WANs)only provide point-to-point communications, use a narrow bandwidth, andoften exhibit heavy communication traffic. Moreover, WANs requirerelatively higher transmission power—a negative factor in the everincreasing need for power savings associated with portable transceivingdevices. As a result, WANs are generally slow and expensive, and simplydo not provide an effective overall solution.

The need for portable, or otherwise mobile, devices has led to smaller,lower power designs. Portable computer terminals have achieved such sizeand power reductions by decreasing local processing and storageresources. In contrast, application programs are growing in size andfunctionality, requiring more and more processing and storage resourcesto operate. As a result, portable computer terminals have beeneffectively disabled from independently performing many needed tasks.Others have been stretched to a nearly unacceptable limit ofportability, battery life and processing and storage ability.

To address such needed tasks, remote processing and storage techniquesare currently being used. For example, stationary remote host computershaving superior processing and storage capability are often connectedvia a WAN network to a mobile computer terminal. In such configurations,whenever the mobile terminal desires access to data, it sends a requestacross the WAN for such data. Similarly, when it desires remoteprocessing, the mobile computer terminal formulates a request which issent to the host computer over the WAN. However, the mobile terminal isstill required to use the relatively expensive and delayed servicesprovided by the WAN for each such request, which often proveunacceptable for a given task.

Similarly, the relaying of communications through even lower power radionetworks is required in many multi-hop radio environments. Repetitiverequests and associated delivery of data, program or processingresources from a source (e.g., a mobile computer terminal) to adestination (e.g., a host computer) takes its toll on overall networkperformance.

Thus, there is a need for a wireless communication network that providesefficient distribution and utilization of network resources in supportof portable and otherwise mobile computer devices.

Yet another object of the invention is to provide a method and apparatuswherein collisions are minimized in overlapping coverage areas byutilizing uncommon communication channel characteristics in a multiplebase station network, while still providing seamless communication forroaming devices by informing roaming devices of the nature of theneighboring base station communication channel characteristics.

A still further object of the present invention is to provide ahierarchical communications system for providing an efficientcommunication pathway for data and programming objects.

Other objects, advantages, and novel features of the present inventionwill become apparent from the following detailed description of theinvention when considered in conjunction with the accompanying drawings.

SUMMARY OF THE INVENTION

The present invention solves many of the foregoing problems in a varietyof embodiments. The network of the present invention has a plurality ofcomputing devices at least one of which is a mobile terminal deviceconfigured with a wireless transceiver. The network comprises aplurality of access devices arranged in a spanning tree configuration tosupport communications among the plurality of computing devices, and atleast one of the plurality of access devices is configured toselectively intercept, store and forward requested data, therebyreducing traffic on the communication network. Further, at least one ofthe plurality of access devices may be configured to selectivelyintercept and store requested processing resources for futureprocessing, again reducing traffic on the communication network. Theprocessing resources stored may be, for example, those that perform thefunction of decoding signals representative of two-dimensional imagescaptured by a two-dimensional code reading device. In addition, at leastone of said plurality of access devices may be configured to selectivelyintercept, store and forward requested program code, once again reducingtraffic on the communication network.

Before storing requested data, processing resources, or program code, anaccess device may consider a number of factors including the cost ofre-obtaining the requested data, processing resources, or program code,the frequency that the data, processing resources, or program code isrequested, the amount of its available storage capacity, and the size ofthe data, processing resources, or program code.

The access device may selectively delete stored data, etc. and mayconsider the factors listed above before doing so.

In another embodiment, a communication network of the present inventionhas a mobile terminal device configured with a wireless transceiver. Thecommunication network also comprises a data source and a plurality ofaccess devices. The plurality of access devices are arranged to providea communication pathway between the mobile terminal device and thecomputing device. Moreover, at least one of said plurality of accessdevices is configured to monitor communication traffic through thataccess devices, and to selectively store for future forwarding requesteddata so as to shorten the communication pathway from the data to themobile terminal device.

In yet another embodiment of the present invention, a communicationnetwork contains at least one two-dimensional code reading deviceconfigured with a first wireless transceiver. The network also comprisesa plurality of access devices arranged to maintain wirelesscommunication with the code reading device. Further, at least one of theplurality of access devices comprising a second wireless transceiver forreceiving signals representative of two-dimensional images captured by atwo-dimensional code reading device, and a code processing circuit fordecoding the received signal.

In another embodiment, in a communication network having at least onetwo-dimensional code reading device configured with a first wirelesstransceiver, a processing device comprises a second wireless transceiverfor receiving signals representative of two-dimensional images capturedby a two-dimensional code reading device. The processing device alsocomprises a code processing circuit for decoding the signals receivedfrom the two-dimensional code reading device. The code processingcircuit delivers to the two-dimensional code reading device via thesecond wireless transceiver an indication of successful image decoding.

The processing device may further comprise an image database for storingsignals representative of two-dimensional images. Such images are usedby the processing circuit for comparison with recieved signals so as toaid in the code identification process. A decode algorithm might also beused, either alone or in combination with attempted identificationthrough image database comparison.

In another embodiment, a communication network operates between apremises and a vehicle which comprising a data source located (at thepremises) and a terminal device (within the vehicle). A firstcommunication link exists between the data source and the terminaldevice. In addition, a vehicular network is included which comprises aportable computing device and the terminal device which communicate viaa second wireless communication link. The terminal device is configuredto store data delivered from the data source, and, upon communicationfrom the portable computing device, selectively forwarding the storeddata to the portable computing device.

Moreover, in some configurations, the terminal device also monitors theflow of data to the portable computing device, and, based on suchmonitoring, said terminal device selectively migrates data into localstorage. Similarly, in other configurations, the terminal device alsomonitors the flow of program code to the portable computing device, and,based on such monitoring, said terminal device selectively migratesprogram code into local storage. In yet other configurations, theterminal device monitors processing requests from the portable computingdevice, and, based on such monitoring, said terminal device selectivelymigrates programming resources into local storage.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a diagrammatic illustration of a hierarchal communicationsystem built in accordance with the present invention.

FIG. 1B is a diagrammatic illustration of another hierarchalcommunication system built in accordance with the present invention.

FIG. 1C is a diagrammatic illustration of still another hierarchalcommunication system built in accordance with the present invention.

FIG. 2 illustrates an embodiment of a basic access interval structureused by a hierarchical network of the present invention.

FIGS. 3A and 3B illustrate the frequency of operation periodicallychanging corresponding to access interval boundaries in a frequencyhopping communication protocol of the present invention.

FIGS. 4A and 4B illustrate more than one access interval being used perhop in a frequency hopping communication protocol of the presentinvention.

FIG. 5A illustrates an embodiment of an access interval used by thehierarchical network of the present invention wherein a reservationphase is Idle Sense Multiple Access.

FIG. 5B illustrates an embodiment of an access interval used by thehierarchical network of the present invention wherein a device responsefollows a reservation poll.

FIG. 6A illustrates an embodiment of an access interval used by thehierarchical network of the present invention having multiplereservation slots for transmission of a Request For Poll signal.

FIG. 6B illustrates an embodiment of an access interval used by thehierarchical network of the present invention wherein general devicescontend for channel access.

FIG. 7A illustrates a sequence in an access interval used by thehierarchical network of the present invention for transferring data froma remote device to a control point device.

FIG. 7B illustrates a sequence in an access interval used by thehierarchical network of the present invention for transferring data froma control point device to a remote device.

FIG. 8 illustrates a preferred embodiment of an access interval used bythe hierarchical network of the present invention.

FIGS. 9A and B conceptually illustrate how multiple NETs may be employedin an idealized cellular-type installation according to the presentinvention.

FIG. 10 illustrates an access point coverage contour overlap for themultiple NETs Infrastructured Network of FIG. 1.

FIG. 11 illustrates hopping sequence reuse in a multiple NETconfiguration of the present invention.

FIG. 12 illustrates a hierarchical infrastructured network of thepresent invention wherein a wireless link connects access points onseparate hard wired LANs.

FIG. 13 illustrates a hierarchical infrastructured network of thepresent invention including a wireless access point.

FIG. 14 illustrates conceptually access points communicating neighboringaccess point information to facilitate roaming of portable/mobiledevices.

FIG. 15 illustrates a secondary access interval used in the MicroLAN orperipheral LAN in the hierarchical communication network according tothe present invention.

FIG. 16 is a flow chart illustrating the selection of an access point bya mobile computing device for communication exchange.

FIG. 17 is a flow chart illustrating a terminal maintainingsynchronization with the network after it has gone to sleep for severalaccess intervals.

FIG. 18 is a flow chart illustrating a terminal maintaining or achievingsynchronization with the network after it has gone to sleep for severalseconds.

FIGS. 19A and 19B are flow charts illustrating an access interval duringinbound communication.

FIGS. 20A and 20B are flow charts illustrating an access interval duringoutbound communication.

FIG. 21 illustrates a sequence in an access interval used in thehierarchical communication network of the present invention with TimeDivision Multiple Access slots positioned at the end of the accessinterval.

FIG. 22 illustrates a sequence in an access interval used by thehierarchical network of the present invention with the Time DivisionMultiple Access slots positioned immediately following the SYNC.

FIG. 23 illustrates a sequence in an access interval used by thehierarchical network of the present invention with the Time DivisionMultiple Access slots positioned immediately following the SYNC andReservation Poll.

FIG. 24 illustrates another sequence in an access interval used by thehierarchical network of the present invention with the Time DivisionMultiple Access slots positioned immediately following the SYNC.

FIG. 25 illustrates a portion of an access interval including thepreamble, SYNC and Reservation Poll.

FIG. 26 illustrates the information contained in a sample SYNC message.

FIG. 27 illustrates the information contained in a sample ReservationPoll.

FIG. 28A illustrates a warehouse environment incorporating acommunication network which maintains communication connectivity betweenthe various network devices according to the present invention.

FIG. 28B illustrates other features of the present invention in the useof a vehicular LAN which is capable of detaching from the premises LANwhen moving out of radio range of the premises LAN to perform a service,and reattaching to the premises LAN when moving within range toautomatically report on the services rendered.

FIG. 28C illustrate other features of the present invention in the useof a vehicular LAN which, when out of range of the premises LAN, isstill capable gaining access to the premises LAN via radio WANcommunication.

FIG. 29A is a diagrammatic illustration of the use of a peripheral LANsupporting roaming data collection by an operator according to thepresent invention.

FIG. 29B is a diagrammatic illustration of another embodiment of aperipheral LAN which supports roaming data collection by an operatoraccording to the present invention.

FIG. 30 is a block diagram illustrating the functionality of RFtransceivers built in accordance with the present invention.

FIG. 31 is a diagrammatic illustration of an alternate embodiment of theperipheral LAN shown in FIG. 2.

FIG. 32 is a block diagram illustrating a channel access algorithm usedby peripheral LAN slave devices in accordance with the presentinvention.

FIG. 33A is a timing diagram of the protocol used according to thepresent invention illustrating a typical communication exchange betweena peripheral LAN master device having virtually unlimited powerresources and a peripheral LAN slave device.

FIG. 33B is a timing diagram of the protocol used according to thepresent invention illustrating a typical communication exchange betweena peripheral LAN master device having limited power resources and aperipheral LAN slave device.

FIG. 33C is also a timing diagram of the protocol used which illustratesa scenario wherein the peripheral LAN master device fails to service theperipheral LAN slave devices.

FIG. 34 is a timing diagram illustrating the peripheral LAN masterdevice's servicing of both the higher power portion of the premises LANas well as the lower power peripheral LAN subnetwork with a single orplural radio transceivers.

FIGS. 35 and 36 are block diagrams illustrating additional power savingfeatures according to the present invention wherein ranging and batteryparameters are used to optimally select the appropriate data rate andpower level of subsequent transmissions.

FIG. 37 illustrates an exemplary block diagram of a radio unit capableof current participation on multiple LANs according to the presentinvention.

FIG. 38 illustrates an exemplary functional layout of the frequencygenerator of FIG. 37 according to one embodiment of the presentinvention.

FIG. 39 illustrates further detail of the receiver RF processing circuitof FIG. 37 according to one embodiment of the present invention.

FIG. 40 illustrates further detail of the receiver signal processingcircuit of FIG. 37 according to one embodiment of the present invention.

FIG. 41 illustrates further detail of the receiver signal processingcircuit of FIG. 37 according to another embodiment of the presentinvention.

FIG. 42 illustrates further detail of the memory unit of FIG. 37according to one embodiment of the present invention.

FIG. 43 illustrates a software flow chart describing the operation ofthe control processor in controlling the battery powered radio unit toparticipate on multiple LANs.

FIG. 44 is an alternate embodiment of the software flow chart whereinthe control processor participates on a master LAN and, when needed, ona slave LAN.

FIG. 45 illustrates another embodiment of the communication system ofthe present invention as adapted for servicing a retail storeenvironment.

FIGS. 46 a-b illustrate a further embodiment of the communication systemof the present invention which illustrate the use of access servers thatsupport local processing and provide both data and program migration.

FIG. 47 a is a flow diagram which illustrates the functionality of theaccess servers of FIGS. 46 a-b in handling data, processing and directrouting requests.

FIG. 47 b is a flow diagram utilized by the access servers of FIGS. 46a-b to manage the migration of data and program code from a sourcestorage and/or processing device toward an end-point device.

FIG. 48 is a schematic diagram of the access servers of FIGS. 46 a-billustrating an exemplary circuit layout which supports thefunctionality described in relation to FIGS. 47 a-b.

FIG. 49 is a specific exemplary embodiment of an access point in amulti-hop communication network utilized for remote processing of 2-D(two-dimension) code information.

FIG. 50 is a schematic diagram similar to that shown in FIG. 48 whichillustrates the circuit layout used in the access point of FIG. 49 toprocess the 2-D code information.

FIGS. 51 a-b are flow diagrams illustrating the operation of the 2-Dcode processing access point of FIGS. 49-50.

FIG. 52 illustrates the structuring of 2-D code information so as tosupport a hierarchical recognition strategy as used by the access pointof FIGS. 49-50.

FIG. 53 is a diagram illustrating an exemplary 2-D code wherein thehierarchical structure of FIG. 52 is implemented.

FIG. 54 is a flow diagram illustrating the functionality of the accesspoint of FIGS. 49-50 in carrying out the hierarchical recognitionstrategy of FIG. 52.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1A illustrates a hierarchical communication system 10 within abuilding in accordance with the present invention. The illustratedhierarchical communication system 10 includes a local area network (LAN)for maintaining typical communication flow within the building premises,herein referred to as a premises LAN. The premises LAN is designed toprovide efficient end-to-end routing of information among hardwired andwireless, stationary and roaming devices located within the hierarchicalcommunication system 10.

The premises LAN consists of an infrastructure network comprising radiobase stations, i.e., wireless access points 15, and a data base server16 which may be part of a more extensive, wired LAN (not shown). Herein,base stations which participate in routing and relaying data throughoutthe communication network are referred to as “access points.” If theyalso participate in the storage or migration of data and program code orin local processing, the base stations are referred to herein as “accessservers.” As will become apparent below, an access point may be modifiedwith additional circuitry and/or programming resources to become anaccess server. Additionally, access servers and access points are bothreferred to herein as “access devices.”

The access points 15 may communicate with each other via hard-wiredlinks, such as Ethernet, RS232, etc., or via wireless (radio frequency)links. A plurality of roaming terminal devices, such as a roamingcomputing device 20, participate in the premises LAN of the hierarchicalcommunication network 10 to exchange information with: 1) other roamingcomputing devices; 2) the data base server 16; 3) other devices whichmight be associated with data base server 16 (not shown); and 4) anyother devices accessible via the premises LAN (not shown). A roamingcomputing device can be, for example, a hand-held computer terminal orvehicle mounted computer terminal (vehicle terminal).

In most circumstances, the premises LAN provides a rather optimalsolution to the communication needs of a given network. However, in somecircumstances, to serve a variety of particular communication needs, thepremises LAN does not offer the optimal solution. Instead of relying onthe premises LAN for such communications, when and where beneficial,alternate LANs are spontaneously created by (or with) network devices,such as the roaming computing device 20, within the hierarchicalcommunication system 10. Such spontaneously created LANs are referred toherein as spontaneous LANs. After the immediate benefits end, i.e., atask has been completed, or if the participants of the spontaneous LANmove out of range of each other, the spontaneous LAN terminatesoperation.

An exemplary spontaneous LAN involves the use of peripheral devices asillustrated in FIG. 1A. Although bulk data transfer destined for aperipheral device 23, such as a printer, from the roaming computingdevice 20 might be communicated through the premises LAN, a more directinterconnection proves less intrusive, saves power, and offers a lowercost solution. Specifically, instead of communicating through thepremise LAN, the roaming computing device 20 needing to print: 1)identifies the presence of an available printer, the peripheral device23; 2) establishes an RF link (binds) with the peripheral device 23; 3)directly begins transferring the bulk data for printing; and 4) lastly,when the roaming terminal finishes the transfer, the spontaneous LANwith the peripheral device 23 terminates. A spontaneous LAN createdbetween the computing devices and peripheral devices is herein referredto as a peripheral LAN. Other types of spontaneous LANs, such asvehicular LANs, are also possible. Embodiments described below identifyvehicular LANs and wide area radio networks (WANs) which are part of thehierarchical communication system according to the present invention.

Although a spontaneous LAN may operate completely independent of thepremises LAN, it is more likely that there will be some degree ofcoordination between the two. For example, while participating in theperipheral LAN, the roaming computing device 20 may terminateparticipation in the premises LAN, and vice versa. Alternately, theroaming computing device 20 may only service the peripheral LAN whenspecific participation on the premises LAN is not required, or viceversa. Moreover, the roaming computing device 20 may attempt to serviceeach peripheral LAN as necessary in a balanced time-sharing fashion,placing little priority upon either LAN. Thus, based on the protocolsand hardware selected, a spontaneous LAN can be configured so as toexist hierarchically above, below, at the same level, or independent ofthe premises LAN.

In generally, to design a given LAN configuration, only thecharacteristics of that LAN are considered for optimization purposes.However, in the hierarchical communication system of the presentinvention, the operation of other LANs must also be taken into account.For example, because of the roaming computing devices participation inboth the premises and peripheral LANs, the requirements and operation ofthe premises LAN must be taken into consideration when defining theperipheral LAN, and vice versa. Thus, the hierarchical communicationsystem of the present invention provides a series of tightly coupledradio LANs and WANs with radio transceiver and communication protocoldesigns which take into consideration such factors as cost, weight,power conservation, channel loading, response times, interference,communication flow, etc., as modified by a primary factor of multipleparticipation.

The peripheral LAN replaces hard-wired connection between a roamingcomputing device and associated peripherals. In a typical configuration,a peripheral LAN will consist of one or more peripherals slaved to asingle master roaming computing device, although multiple master roamingcomputing devices are possible. Peripheral devices may be printers, codescanners, magnetic card readers, input stylus, etc.

Each of the peripheral devices 22 has a built-in radio transceiver tocommunicate with the roaming computing devices 20. The roaming computingdevices 20 are configured with built-in radio transceivers capable ofcommunicating on both the peripheral and premises LAN. The access points15 may be configured with radio transceivers only capable ofcommunicating in the premises LAN. In alternate embodiments, asdescribed below, the access points 15 might instead be configured toparticipate on both the premises and peripheral LANs.

In particular, the peripheral LAN is intended to provide communicationsbetween two or more devices operating within near proximity, e.g.,distances of a few tens of feet. The majority of constituents of theperipheral LAN are generally devices that do not require access toresources outside their immediate group, or which can suffice withindirect access through devices which participate outside theirimmediate peripheral LAN group. In contradistinction, the premises LANis intended to provide communications between relatively many devicesoperating across great distances throughout a building.

The characteristics of the peripheral LAN permit the use of radiotransceivers of lower cost, lower power consumption, and generally moresimplistic operation than permitted by the premises LAN. However, theoperation of the peripheral LAN is adapted for integration with thepremises LAN so that a radio transceiver and protocol designed foroperation on the premises LAN includes features which allow concurrentor sequentially concurrent operation on the peripheral LAN. For example,by selecting similar communication hardware characteristics andintegrating protocols, communication within the premises and peripheralLANs may be achieved with a single radio transceiver.

In one embodiment, radio communication through the premises LAN, i.e.,among the access points 15 and the roaming computing device 20, utilizesrelatively higher-power spread-spectrum frequency-hopping communicationwith a reservation access protocol. The reservation access protocolfacilitates frequency-hopping and supports adaptive data rate selection.Adaptive data rate selection is based upon the quality of communicationon the premises LAN radio channel. Radio communication through theperipheral LAN utilizes a relatively lower-power single frequencycommunication also with a reservation access protocol. As more fullydescribed below, the coordinated use of reservation access protocols inthe peripheral and premises LANs maximize information flow whileminimizing conflicts between devices participating in the two LANs.

Referring to FIG. 1B, a small hierarchal communication system 30 builtin accordance with the present invention is shown. An access point 33and two roaming or mobile computing devices 35 and 36 form a premisesLAN 37. The premises LAN 37 provides for communication among the mobilecomputing devices 35 and 36 and a host computer 34. The mobile computingdevices 35 and 36 can roam anywhere within the range of the access point33 and still communicate with the host computer 34 via the access point33.

Two peripheral LANs 40 and 41 allow for wireless communication betweeneach mobile computing device 35 and 36 and its respective peripheraldevices 43, 44 and 45 when the mobile computing device is notcommunicating on the premises LAN 37. Specifically, the peripheral LAN40 consists of the mobile computing device 35 and the peripheral device43, while the peripheral LAN 41 consists of the mobile computing device36 and the two peripheral devices 44 and 45.

FIG. 1C illustrates another embodiment according to the presentinvention of a larger hierarchal communication system 50. The hostcomputer 55 is connected to access points 56, 57, 58 and 59. The hostcomputer 55 and the access points 56, 57, 58 and 59 provide theinfrastructure for the premises LAN. The access points need not behard-wired together. For example, as illustrated in FIG. 1C, the accesspoints 56, 57 and 58 access each other and the host computer 55 via ahard-wired link, while the access point 59 accomplishes such access viaa wireless link with the access point 58.

The access points 56, 58 and 59 can support multiple mobile computingdevices. For example, the access point 56 uses a frequency-hoppingcommunication protocol for maintaining communication with mobilecomputing devices 61 and 62. Moreover, each of the mobile computingdevices may roam out of range of the access point with which they havebeen communicating and into the range of an access point with which theywill at least temporarily communicate. Together, the host computer 55and the access points 56, 57, 58 and 59 and mobile computing devices 61,62, 64, 65 and 66 constitute a premises LAN.

More particularly, each access point operates with a different set ofcommunication parameters. For example, each access point may use adifferent frequency hopping sequence. Additionally, different accesspoints may not employ a common master clock and will not be synchronizedso as to have the frequency hopping sequences start at the same time.

Mobile computing devices 61, 62, 64, 65 and 66 are capable of roaminginto the vicinity of any of the access points 56, 58 and 59 andconnecting thereto. For example, mobile computing device 62 may roaminto the coverage area of access point 58, disconnecting from accesspoint 56 and connecting to access point 58, without losing connectivitywith the premises LAN.

Each mobile computing device 61, 62, 64, 65 and 66 also participateswith associated peripherals in a peripheral LAN. Each peripheral LAN ismade up of the master device and its slave device. Similarly, asillustrated, the access point 57 is shown as a direct participant in notonly the premises LAN but also in the peripheral LAN. The access point57 may either have limited or full participation in the premises LAN.For example, the access point 57 may be configured as a mobile computingdevice with the full RF capability of transmission in both the premisesand peripheral LANs. Instead, however, participation in the premises LANmay be limited to communicating through the hard-wired link, effectivelydedicating the access point 57 to the task of servicing peripherals.

Although the use of a plurality of built-in radio transceivers could beused so as to permit simultaneous participation by a single device,factors of cost, size, power and weight make it desirable to onlybuild-in a single radio transceiver capable of multiple participation.Furthermore, even where a plurality of radio transceivers are built-in,simultaneous participation may not be possible depending upon thepotential transmission interference between transceivers. In fact, fullsimultaneous participation may not be desirable at least from aprocessing standpoint when one transceiver, servicing one LAN, always orusually takes precedence over the other. Justification for suchprecedence generally exists in a premises LAN over a peripheral LAN.

For example, communication flow in most premises LANs must be fast,efficient and rather robust when considering the multitude ofparticipants that operate thereon. In the peripheral LAN, however,response times and other transmission related delays are generally moreacceptable—even adding extra seconds to a peripheral printer's printtime will usually not bother the user. Thus, in such communicationenvironments, it may be desirable to design the transmitters andassociated protocols so that the premises LAN takes precedence over theperipheral LAN. This may yield a communication system where fullysimultaneous participation in both the premises and peripheral LANs doesnot exist.

In communication environments wherein fully simultaneous participationdoes not exist or is not desired, transmitter circuitry might be sharedfor participation in both the premises and peripheral LANs. Similarly,in such environments, the communication protocol for the peripheral LANcan be tightly coupled with the protocol for the premises LAN, i.e.,integrated protocols, so as to accommodate multiple participation.Moreover, one protocol might be designed to take precedence over theother. For example, the premises LAN protocol might be designed so as tominimize participation or response time in the peripheral LAN. Asdescribed in more detail below, such transceiver and protocol analysisalso takes place when considering additional multiple participation inthe vehicular LAN and WAN environments.

FIG. 2 illustrates an embodiment of a communication protocol for thepremises LAN which uses a basic Access Interval 200 (“AI”) structureaccording to the present invention. Generally, an Access Interval is thebasic communication unit, a fixed block of time, that allocatesbandwidth to synchronization, media access, polled communications,contention based communications, and scheduled services. The AccessInterval in FIG. 2 includes a SYNC header 201 generated by a ControlPoint (“CP”) device of a NET. The term NET describes a group of users ofa given hopping sequence or a hopping sequence itself. The Control Pointdevice is generally the access point 15 referenced above with regard toFIG. 1. The SYNC header 201 is used by constituents of the NET to attainand maintain hopping synchronization. A reservation phase 203 followspermitting a reservation poll, which provides the NET constituents anopportunity to gain access to media. A sessions frame 205 is nextallocated for communication protocol. A frame 207 follows for optionaltime division multiple access (“TDMA”) slots in order to accommodatescheduled services. Scheduled services, for example, real time voice orslow scan video, are such that they require a dedicated time slot toprovide acceptable quality of service. The function of frames 201, 203,205 and 207 will be discussed in greater detail below.

As was shown in FIG. 2, FIG. 21 illustrates a sequence in an accessinterval 2100 with the Time Division Multiple Access slots 2113positioned at the end of the access interval 2100. In present example,if this were also a HELLO interval, the HELLO would immediately followthe SYNC 1201. Location of the Time Division Multiple Access slots atsuch a position provides certain advantages including, for example, 1)the SYNC 2101, HELLO (not shown), Reservation Poll 2103, may all becombined into a single transmission (concatenated frames); 2) hoppinginformation may be moved to or included in the Reservation Poll 2103allowing for a shorter preamble in the SYNC 2101; and 3) the HELLOmessages will occur early in the Access Interval 2100 providing forshorter receiver on times for sleeping terminals.

The Time Division Multiple Access slots may also be located at differentpoints within the access interval. Positioning the Time DivisionMultiple Access slots allow for various systemic advantages. Referringnow to FIG. 22, an access interval 2200 is illustrated showing the TimeDivision Multiple Access slots 2203 immediately following the SYNC 2201.Location of the Time Division Multiple Access slots 2203 at thisposition provides certain advantages including, for example, 1) bettertiming accuracy is achieved when the Time Division Multiple Access slots2203 immediately follow the SYNC 2201; 2) Session Overruns do notinterfere with the Time Division Multiple Access slots 2203; 3) deviceswhich do not use the Time Division Multiple Access slots 2203 do notnecessarily need to be informed of the Time Division Multiple Accessslot allocation; and 4) HELLO message may follow Time Division MultipleAccess slots 2203, Reservation Slots 2207 or Reservation Resolution Poll2209.

Referring now to FIG. 23, an access interval 2300 is illustrated showingthe Time Division Multiple Access slots 2305 immediately following theSYNC 2301 and the Reservation Poll 2303. In the present example, if thiswere a HELLO interval, a HELLO message would immediately follow theReservation Resolution Poll 2309.

Location of the Time Division Multiple Access slots 2305 at the positionshown in FIG. 23 provides certain advantages including, for example, 1)the Time Division Multiple Access slot timing is keyed to SYNC 2301 forbetter accuracy; 2) the number of Time Division Multiple Access slots2305 may be indicated in SYNC 2301 or the Reservation Poll 2303,providing greater flexibility; 3) Session frame overruns do notinterfere with Time Division Multiple Access slots 2305; 4) only onemaintenance transmission is required per Access Interval 2300; and 5)hopping information may be moved to or included in the Reservation Poll2303, permitting a shorter preamble in SYNC 2301.

In the access interval 2300 configuration shown in FIG. 23, it ispossible that the Time Division Multiple Access slots 2305 and theresponse slots 2307 could be the same. The Reservation Poll 2303 wouldallocate the correct number of slots and indicate which are reserved forTime Division Multiple Access. For example, to use Idle Sense MultipleAccess 1 slot) with 1 inbound and 1 outbound Time Division MultipleAccess slots, three slots would be allocated with the first two slotsreserved. The appropriate Time Division Multiple Access slot duration is80 bits at a hop rate of 200 hops per second which is just about theexpected duration of a Request for Poll. At slower hop rates, multipleslots could be allocated to Time Division Multiple Access allowing theTime Division Multiple Access slot duration to be constant regardless ofhop rate.

Referring now to FIG. 24, another access interval 2400 is illustratedshowing the Time Division Multiple Access slots 2403 immediatelyfollowing the SYNC 2401. In this example the Poll Message Queue 2405immediately follows the Time Division Multiple Access slots 2403. Theconfiguration shown in FIG. 24 provides for certain advantagesincluding, for example, 1) the Time Division Multiple Access slot timingis keyed to SYNC 2401 for better accuracy; and 2) Session frame overrunsdo not interfere with Time Division Multiple Access slots 2403.

The configurations shown in FIG. 21 and in FIG. 23 are preferred becausethey allow the Reservation Poll messages to be transmitted immediatelyfollowing the SYNC and because of the power management and interferencereduction advantages.

In one embodiment of the Access Interval structure, all messagetransmissions use standard high-level data link control (“HDLC”) dataframing. Each message is delimited by High-Level Data Link ControlFlags, consisting of the binary string 01111110, at the beginning of themessage. A preamble, consisting of a known data pattern, precedes theinitial FLAG. This preamble is used to attain clock and bitsynchronization prior to start of data. Receiver antenna selection isalso made during the preamble for antenna diversity. A CRC for errordetection immediately precedes the ending FLAG. Data is NRZ-I(differentially) encoded to improve data clock recovery. High-Level DataLink Control NRZ-I data is run-length-limited to six consecutive bits ofthe same state. Alternatively, a shift register scrambler could beapplied instead of differential encoding to obtain sufficienttransitions for clock recovery. Data frames may be concatenated, withtwo or more frames sent during the same transmission, with a single FLAGseparating them. An example of this is SYNC, followed by a HELLO orReservation Poll (SYNC, HELLO and Reservation Poll are discussed morefully below).

While much of the following discussion centers on the use of frequencyhopping in the premises LAN, the Access Interval structure of thepresent invention is also suitable for single channel and directsequence spread spectrum systems. The consistent timing of channelaccess, and the relative freedom from collisions due to channelcontention, provide desirable benefits in systems that support portable,battery powered devices regardless of modulation type or channelization.Functions that are unique to frequency hopping may be omitted if otherchannelization approaches are used.

FIGS. 3 a and 3 b illustrate the frequency of operation periodicallychanging corresponding to Access Interval boundaries in a frequencyhopping system. Frequency hopping systems use a hopping sequence, whichis a repeating list of frequencies of length (n) selected in a pseudorandom order and is known to all devices within a coverage area. FIG. 3a illustrates a frequency hopping system having one Access Interval 301per frequency hop (the hop occurring every 10 milliseconds) and a lengthof 79. FIG. 3 b illustrates a frequency hopping system having one AccessInterval 303 per frequency hop (the hop occurring every 20 milliseconds)and a length of 79. The 20 ms time frame is preferred for a protocolstack that uses a maximum network layer frame of up to 1536 bytespayload while maintaining two real time voice communications channels.Access interval duration may be optimized for other conditions. AccessInterval length is communicated to the NET during the SYNC portion ofthe Access Interval. This allows Access Interval duration, and other NETparameters to be adjusted without reprogramming every device within theNET.

The Access Interval is a building block. The length of the AccessInterval can be optimized based on network layer packet size, expectedmix of Bandwidth on Demand (“BWOD”) and Scheduled Access traffic,expected velocities of devices within the NET, acceptable duration ofchannel outages, latency or delay for scheduled services, etc. Thepreferred Access Interval duration of 20 ms (and maximum packet lengthof 256 Bytes at 1 MBIT/sec) represents a value chosen for systems withdevice velocities up to 15 MPH, and a mix between Bandwidth On Demandand scheduled service traffic.

Within a frequency hopping network, one or more Access Intervals may beused during each dwell in a frequency hopping system. A dwell is thelength of time (d) each frequency in the hopping sequence is occupied bythe system. For example, FIGS. 4 a and 4 b show illustrations of caseswhere more than one 20 ms Access Interval 401 is used per hop. This maybe appropriate for some instances where it is undesirable to hop athigher rates because of relatively long frequency switching times of theradio hardware, where import, export, or regulatory restrictionsdisallow hopping at a faster rate, or in some applications where it isdesirable to maintain operation on each channel for a longer period. Anexample of the latter is the case where larger files or data records aretransferred routinely.

In a frequency hopping operation, the Access Interval 200 of FIG. 2begins with a SYNC header 201. As mentioned above, the SYNC is generatedby the Control Point (CP) device of the NET. The SYNC is used byconstituents of the NET to attain and maintain hopping synchronization.Included in the SYNC are:

-   -   1. Address of the Control Point device.    -   2. Identification of the Hopping Sequence, and index of the        current frequency within the hop table.    -   3. Identification of the hop rate, number of Access Intervals        per hop, and Access Intervals before next hop.    -   4. A timing character for synchronization of device local clocks        to the NET clock contained within the Control Point device.    -   5. Status field indicating reduced SYNC transmissions due to low        NET activity (Priority SYNC Indicator).    -   6. Status field indicating if the Access Interval will contain a        broadcast message to all devices within the NET.    -   7. Status field indicating premises or spontaneous LAN        operation.    -   8. The SYNC field information is optionally encrypted using a        block encryption algorithm, with a key provided by the network        user. A random character is added to each SYNC message to        provide scrambling.

However, there are two circumstances during which a SYNC message is nottransmitted: 1) co-channel interference; and 2) low NET utilization.With regard to co-channel interference, before issuing a SYNC message,the Control Point device performs channel monitoring for a briefinterval. If the Received Signal Strength Indicator (RSSI) levelindicates an ON channel signal greater than the system defer threshold,then the Access Interval is skipped. Alternatively, a strong ON channelsignal may dictate a reduction in Control Point device power to limitthe interference distance of the net for the duration of the AccessInterval. A system defer threshold 30 dB above the receiver sensitivityis a preferred choice. Communication within the NET is deferred for theduration of the Access Interval if SYNC is not transmitted due toco-channel interference.

In times of low system utilization, SYNC and Reservation Poll messagesare reduced to every third Access Interval. The SYNC message includes astatus field indicating this mode of operation. This allows devices toaccess the NET, even during Access Intervals where SYNC is skipped, byusing an Implicit Idle Sense algorithm. If the hopping sequence is 79frequencies in length as shown in FIGS. 3 a and 3 b, use of every thirdAccess Interval guarantees that a SYNC message will be transmitted oneach frequency within the hopping sequence once each three cycles of thesequence, regardless of whether 1, 2 or 4 Access Intervals occur eachhop dwell. This addresses US and European regulatory requirements foruniform channel occupancy, and improves the prospects forsynchronization of new units coming into the NET during periods when theNET is otherwise inactive. SYNC messages that are on multiples of 3Access intervals are labeled as priority SYNC messages. “Sleeping”terminals use priority SYNCs to manage their internal sleep algorithms.Sleeping terminals and Implicit Idle Sense are discussed in more detailbelow.

It should be noted that SYNC messages are preceded by dead time, whichmust be allocated to account for timing uncertainty between NET clocksand local clocks within NET constituents. In frequency hopping systems,the dead time must also include frequency switching time for the RFmodem.

The Reservation Poll frame 203 immediately follows the SYNC header 201.The two messages are concatenated High-Level Data Link Control framesseparated by one or more Flags. The reservation poll provides NETconstituents an opportunity to gain access to the media. It includes:

-   -   1. A field specifying one or more access slots.    -   2. A field specifying a probability factor between 0 and 1.    -   3. A list of addresses for which the access points has pending        messages in queue.    -   4. Allocation of Time Division Multiple Access slots for        scheduled services by address.    -   5. Control Point device Transmitted Power level for SYNC and        Reservation Polls.

The number of access slots, n, and the access probability factor, p, areused by the Control Point device to manage contention on the channel.They may each be increased or decreased from Access Interval to AccessInterval to optimize access opportunity versus overhead.

If the NET is lightly loaded, the pending message list is short, and theNET is not subject to significant interference from other nearby NETs,the control point device will generally specify a single slot 501 asshown in FIG. 5 a, with a p factor <1. In this case, the reservationphase is Idle Sense Multiple Access (“ISMA”). Devices with transmissionrequirements that successfully detect the Reservation Poll will transmita Request for Poll (“RFP”) with probability p and defer transmissionwith probability 1-p. FIG. b shows a device response (address 65 503following the reservation poll.

In cases when the transmission density is higher, n multiple reservationslots will be specified, generally with a probability factor p of 1. Inthis case a device will randomly choose one of n slots for transmissionof their Request for Poll. The slotted reservation approach isparticularly appropriate in instances where many NETs are operating innear proximity, since it diminishes reliance on listen before talk(“LBT”) (explained more fully below). The number of slots n isdetermined by a slot allocation algorithm that allocates additionalslots as system loading increases. FIG. 6 a shows multiple slots 601.

In cases where NET loading is extreme, the Control Point may indicate anumber of slots, e.g., not more than 6, and a probability less than 1.This will cause some number of devices to defer responding with aRequest for Poll in any of the slots. This prevents the control pointdevice from introducing the overhead of a large number of slots inresponse to heavy demand for communications, by dictating that someunits back off until demand diminishes.

A pending message list is included in the Reservation Poll. The pendingmessage list includes the addresses of devices for which the ControlPoint device has messages in queue. Devices receiving their address maycontend for the channel by responding with a Request For Poll (RFP) inthe slot response phase. FIG. 6 b shows several devices 603, 605 and 607contending for channel access. Messages that the Control Point devicereceives through the wired infrastructure that are destined for Type 1devices, and inactive Type 3 devices whose awake window has expired, areimmediately buffered, and the device addresses are added to the pendingmessage list. When a message is received through the infrastructure fora Type 2 device, or an active Type 3 device, their address isprioritized at the top of the polling queue. (Device Types and pollingqueue are described below.) The pending message list is aged over aperiod of several seconds. If pending messages are not accessed withinthis period, they are dropped.

Devices with transmission requirements respond in slots with a Requestfor Poll. This message type includes the addresses of the Control Pointdevice and requesting device, the type and length of the message it hasto transmit, and a field that identifies the type of device. Devicesthat detect their address in the pending message list also contend foraccess in this manner.

As mentioned above, devices may be Type 1, Type 2, or Type 3. Type 1devices are those which require critical battery management. These maybe in a power saving, non-operational mode much of the time, onlyoccasionally “waking” to receive sufficient numbers of SYNC andReservation Poll messages to maintain connectivity to the NET. Type 2devices are those that are typically powered up and monitoring the NETat all times. Type 3 units are devices that will remain awake for awindow period following their last transmission in anticipation of aresponse. Other device types employing different power managementschemes may be added.

Slot responses are subject to collision in both the single and multipleslot cases. Collisions may occur when two or more devices attempt tosend Request for Polls in the same slot. However, if the signal strengthof one device is significantly stronger than the others, it is likely tocapture the slot, and be serviced as if it were the only respondingunit. FIG. 6 b shows two devices 605, address 111, and 607, address 02,that may be subject to collision or capture.

The Control Point device may or may not be able to detect collisions bydetecting evidence of recovered clock or data in a slot, or by detectingan increase in RF energy in the receiver (using the Received SignalStrength Indicator, (“RSSI”)) corresponding to the slot interval.Collision detection is used in the slot allocation algorithm fordetermining addition or deletion of slots in upcoming Reservation Polls.

As an optional feature to improve collision detection in the multipleslot case, devices that respond in later slots may transmit theaddresses of devices they detect in earlier slots as part of theirRequest for Poll. Request for Polls which result in collisions at theControl Point device often are captured at other remote devices, sincethe spatial relationship between devices that created the collision atthe base does not exist for other device locations within the NET. Theduration of the response slots must be increased slightly to providethis capability.

If the Control Point device receives one or more valid Request for Pollsfollowing a Reservation Poll, it issues a Reservation Resolution (“RR”)Poll and places the addresses of the identified devices in a pollingqueue. The Reservation Resolution message also serves as a poll of thefirst unit in the queue. Addresses from previous Access Intervals andaddresses of intended recipients of outbound messages are also in thequeue.

If the Polling Queue is empty, then no valid Request for Polls werereceived or collision detected and no Reservation Resolution poll isissued. If within this scenario a collision is detected, a CLEAR messageindicating an Explicit Idle Sense (explained more fully below) istransmitted containing a reduced probability factor to allow collidingunits to immediately reattempt NET access.

Outbound messages obtained through the network infrastructure may resultin recipient addresses being prioritized in the queue, that is, if therecipients are active devices—Type 2 devices or Type 3 devices whoseawake window has not expired. This eliminates the need for channelcontention for many outbound messages, improving efficiency. Messagesfor Type 1 devices are buffered, and the recipient address is placed inthe pending message list for the next Access Interval.

Generally the queue is polled on a first in first out (FIFO) basis. Thepolling order is:

a. Addresses of active units with outbound messages.

b. Addresses from previous Access Intervals

c. Addresses from the current Access Interval

Since propagation characteristics vary with time and operatingfrequency, it is counterproductive to attempt retries if Poll responsesare not received. If a response to a Poll is not received, the nextaddress in the queue is polled after a short response time-out period.Addresses of unsuccessful Polls remain in the queue for Polling duringthe next Access Interval. Addresses are aged, so that after severalunsuccessful Polls they are dropped from the queue. Addresses linked tooutbound messages are added to the pending message list. Devices withinbound requirements must re-enter the queue through the nextreservation phase.

Data is transferred in fragments. A maximum fragment payload of 256bytes is used in the preferred implementation. If transfer of networkpackets larger than of 256 bytes is required, two or more fragments aretransferred. Fragments may be any length up to the maximum, eliminatingthe inefficiency that results when messages that are not integermultiples of the fragment length are transmitted in systems that employfixed sizes.

The sequence for transferring data from a remote device to the controlpoint device is illustrated in FIG. 7 a. It is assumed that address 65is the first address in the polling queue. The Reservation Resolutionpoll 701 from the control point device includes the device address andthe message length that device 65 provided in its initial Request forPoll. A first fragment 703 transmitted back from device 65 is a fulllength fragment. Its header includes a fragment identifier and a fieldproviding indication of the total length of the message. Lengthinformation is included in most message types during the sessions periodto provide reservation information to devices that may wish to attemptto access the NET following an Explicit Idle Sense (explained more fullybelow).

Following successful receipt of the first fragment, the Control Pointdevice sends a second poll 705, which both acknowledges the firstfragment, and initiates transmission of the second. The length parameteris decremented to reflect that the time required for completion of themessage transfer is reduced. A second fragment 707 is transmitted inresponse, and also contains a decremented length field. Followingreceipt of the second fragment 707, the Control Point device sends athird poll 709. This pattern is continued until a final fragment 711containing an End of Data (EOD) indication is received. In FIG. 7, thefinal fragment is shorter than a maximum length fragment. The ControlPoint device sends a final Acknowledge (ACK), and the device sends afinal CLEAR 713 to indicate conclusion of the transmission. The CLEARmessage contains a probability factor p for Explicit Idle Sense(explained more fully below). The value of p is determined by theControl Point device in the ACK and echoed by the device terminationcommunication. A p of zero indicates that the control point device willbe initiating other communications immediately following receipt of theCLEAR message. A probability other than 0 indicates an Explicit IdleSense.

If for some reason a fragment is not successfully received, the nextpoll from the Control Point device would indicate a REJECT, and requestre-transmission of the same fragment. The length field would remainfixed at the previous value, prolonging reservation of the channel forthe duration of the message. After a fragment is transmitted more thanonce without successful reception, the Control Point device may suspendattempts to communicate with the device based upon a retry limit, andbegin polling of the next address in the queue.

A flow chart depicting how inbound messages are received during anaccess interval is shown in FIGS. 19A and 19B. A flow chart depictinghow outbound messages are transmitted during an access interval is shownin FIGS. 20A and 20B.

Outbound messages are transmitted in a similar fashion as inboundmessages, with the Control Point and device roles largely reversed asillustrated in FIG. 7 b. When the Control Point reaches an address inthe queue for which it has an outbound message, the Control Pointtransmits a Request for Poll 721 identifying the address of the deviceand the length of the message. The response back from the device wouldbe a poll with an embedded length field. The samePOLL/FRAGMENT/ACK/CLEAR structure and retry mechanisms as describedabove with regard to inbound messages in reference to FIG. 7 a aremaintained. The CLEAR from the device indicates a probability p of zero.If the polling queue is empty, the Control Point may send a final orterminating CLEAR 723 containing a probability for Explicit Idle Sense.

All terminating ACK or CLEAR messages contain fields to aid insynchronization of new units to the NET. The content of these fields isidentical to that in the SYNC message, except that the timing characteris deleted. Synchronization is discussed more fully below.

Broadcast Messages intended for groups of addresses, or all addresseswithin a NET may be transmitted during the sessions period. Broadcastmessages are not individually acknowledged. These messages may becommunicated at intervals over the course of several Access Intervals toprovide reliable communication. Messages such as SYNC and ReservationPolls are specialized broadcast messages, with dedicated bandwidth inthe Access Interval structure.

Security of payload data is left to the higher protocol layers.Application programs resident in portable/mobile devices may employencryption or other means of providing protection against undesired useof transmitted data.

Portable/mobile devices may employ transmitter power control during thesessions period to reduce potential interference with other NETs thatmay occasionally be on the same or adjacent channels. These devices willuse Received Signal Strength Indicator readings from outbound messagesto determine if transmitter power may be reduced for their inboundtransmission. Because of the need to maintain channel reservations andListen Before Talk capabilities, the Control Point device does not usetransmitter power control. Since Control Point devices are generallypart of an installed system infrastructure, they are likely to bephysically separated from devices operating in other NETs. They aretherefore less likely to cause interference to devices in other NETsthan portable devices, which may operate in proximity to devices inother NETs.

Often, control point devices will empty the polling queue before theconclusion of the access interval. Two mechanisms within the AccessControl Protocol, Explicit and Implicit Idle Sense, are provided toimprove bandwidth utilization. These supplemental access mechanismsoften provide means for devices that failed to gain reservations duringthe reservation phase to gain access to the NET within the AccessInterval. To assume an Explicit or Implicit Idle Sense, a device musthave detected a valid SYNC and Reservation Poll in the current AccessInterval.

The incorporation of a probability factor p≠0 in the final (terminating)ACK or CLEAR from the control point device provides the function of anExplicit Idle Sense (mentioned above). Devices with transmissionrequirements solicit Request for Polls using the same rules normallyused for a single slot Reservation Poll. Successfully identifiedaddresses are placed in the polling queue, and are polled immediately orin the next Access Interval depending on the time remaining in thecurrent Access Interval. The p factor for Explicit Idle Sense is subjectto the same optimization algorithm as the Reservation Poll probability.

Communication of channel reservations, in the form of the length fieldsin Polls and Message Fragments is useful to units seeking to access theNET through Explicit Idle Sense. Reservations allow devices topredictably power down during the period that another device hasreserved the NET to conserve battery power, without loosing the abilityto gain access to the NET.

Implicit Idle Sense provides an additional means of channel access. AnImplicit Idle Sense is assumed whenever a device detects a quietinterval period greater than or equal to the duration of a Poll plus themaximum fragment length after a channel reservation has expired.Detection based upon simple physical metrics, such as a change inReceived Signal Strength Indicator or lack of receiver clock recoveryduring the quiet interval, are preferred methods of ascertaining channelactivity. Algorithms based upon these types of indicators are generallyless likely to provide a false indication of an inactive channel thanthose that require successful decoding of transmissions to determinechannel activity. False invocation of an Implicit Idle Sense is the onlymechanism by which data transmissions are subject to collision withinthe NET. Thus, the Implicit Algorithm must be conservative.

Quiet interval sensing may begin at the following times within theAccess Interval:

-   -   a. Any time after the last reservation slot following a        Reservation Poll;    -   b. Any time after a terminating ACK or CLEAR indicating an        Explicit Idle Sense;    -   c. Following an unsuccessful response to a single Slot        Reservation Poll; or    -   d. Any time prior to reserved Time Division Multiple Access time        slots at the end of the Access Interval.

It is preferable that devices detecting a quiet interval use a ppersistent algorithm for channel access to avoid collisions. Theprobability factor for Implicit Idle Sense Access will generally be lessthan or equal to the factor in Explicit Idle Sense.

A device must receive the SYNC and Reservation Polls at the beginning ofan Access Interval to use Implicit Idle Sense. The Reservation Pollprovides indication of guaranteed bandwidth allocation to scheduledservices at the end of the Access Interval, which may shorten the periodavailable for Bandwidth On Demand communications.

Devices requiring scheduled services must contend for the channel in thesame fashion as those requiring Bandwidth On Demand access. When polled,these initiating devices will initiate a connection request thatindicates the number of inbound and outbound Time Division MultipleAccess slots required for communication, and the address of the targetdevice with which communication is desired. The network infrastructurewill then attempt to establish the connection to the target device. Oncethe connection is established, the Control Point device will signal theallocation of slots to the initiating device. Time Division MultipleAccess slots are relinquished by transmitting a disconnect message tothe control point device in the Time Division Multiple Access slot untilthe disconnect is confirmed in the next Reservation Poll.

The transmission requirements of speech and slow scan video (scheduledservices) are similar. In one embodiment, Time Division Multiple Accessslots are allocated as multiples of 160 bits payload at 1 MBIT/sec, plusoverhead for a total of 300 μs. For 10 ms access intervals, acceptablevoice communication can be obtained by allocating 1 Time DivisionMultiple Access slot each for inbound and outbound communication peraccess interval. For 20 ms access intervals, two slots each way arerequired. A system employing 10 ms access intervals at 100 hops persecond may improve transmission quality by using two or three slots eachAccess Interval and sending information redundantly over two or threeaccess intervals using interleaved block codes. Scheduled transmissionsare generally not subject to processing or validation by the controlpoint device, and are passed through from source to destination. Use ofinterleaved error correction coding or other measures to improvereliability are transparent to the NET.

The selection of certain system parameters are important whenconsidering scheduled services. As an example, since speech is quantizedover the duration of the access interval and transmitted as a burst, thelength of the access interval translates directly into a transport delayperceptible to the recipient of that speech. In real time voicecommunications, delays longer than 20 ms are perceptible, and delayslonger than 30 ms may be unacceptable. This is particularly the casewhere the premises LAN is interconnected with the public switchedtelephone network (“PSTN”), which introduces its own delays. Two wayservices such as voice communications are the most sensitive totransport delay because delay impacts the interaction of thecommunicating parties. One way services are less sensitive to transportdelay. One way services are good candidates for interleaving or otherforms of redundant transmission.

Similarly, the selection of hop rate is important, as hop ratedetermines the duration of outages that may occur. If one or morefrequencies in the hop sequence are subject to interference, forinstance, scheduled transmissions during those hops will be disrupted.In a system that hops slowly, detrimental outages of hundreds ofmilliseconds will occur resulting in poor transmission quality.Occasional losses of smaller durations, e.g., 10 ms or 20 ms, aregenerally less perceptible, indicating that faster hop rates aredesirable if the NET is to offer real time voice transport.

Scheduled service intervals may also be used for data transport on ascheduled or priority basis. Telemetry, data logging, print spooling,modem replacement, or other functions are possible. For theseactivities, a few Time Division Multiple Access slots scheduled forexample every fourth, eighth, or sixteenth Al are necessary.

Because of multipath and dispersion issues with 2.4 GHz transmission atrelatively high data rates, the ability of the NET to adaptively switchbetween two or more data rates is desirable.

In one embodiment, implementation of data rate switching may beaccomplished by selecting a standard rate of communications, e.g., 250KBPS and high rate of communications of 1 Mbit/sec. Messages thatcontain system status information, including SYNC, Reservation Polls,Reservation Resolution Polls (Request for Polls), Polls, ACKs and CLEARSare transmitted at the standard rate. These messages are generallyshort, and the time required for transmission is largely determined byhardware overhead, e.g., transmitter receiver switching time. Theincremental overhead introduced by transmitting these messages at thelower rate is therefore small in comparison to the total length of anaccess interval. The reliability of reception of these messages willincrease, which will eliminate unnecessary retries in some instanceswhere fragments are received successfully, but acknowledgements or pollsare missed.

A test pattern at the higher data rate is inserted in each Poll (not inReservation Polls, however). The Poll recipient evaluates signal qualitybased on the high data rate test pattern, Received Signal StrengthIndicator, and other parameters to determine whether to transmit afragment at the high rate or the low rate. Fragment lengths are selectedsuch that high and low rate maximum fragment lengths are the sameduration. In other words, a fragment at the low rate conveysapproximately ¼ the payload of a fragment for the case where the datarate is four time greater. This method is generally suitable fortransaction oriented communications, which frequently require shortmessage transmissions. Alternatively, the length field in Polls andmessages can be used to allow different fragment lengths for the twodata rates while still providing channel reservation information toother devices in the NET. This method also provides for forwardmigration. As modulation and demodulation methods improve, newerproducts can be added to old networks by upgrading Control Pointsdevices. Both new and old devices share the ability to communicate at acommon low data rate.

An alternate embodiment uses signaling messages such as SYNC,Reservation Polls, Request for Polls, etc., at the higher rate withfallback operation to the standard rate for the communications sessionsonly SYNC and Reservation Polls at the high rate constitute a high datarate test message. The Request for Poll response to the Reservation Pollat the high rate may include a field indicating that sessionscommunications should take place at the fallback, standard rate. Signalquality measures such as signal strength and clock jitter areappropriate. Data rate selection information is included with the deviceaddress in the polling queue. When the device is polled, it will bepolled at the rate indicated in the Request for Poll. Channelreservation information in the Reservation Resolution Poll will indicatethe reservation duration based upon the data rate indicated.

In this alternate embodiment, the fact that SYNC and Reservation Pollsmust be detectable at the high data rate prioritizes access to the NETfor those devices that have acceptable connectivity during the currentaccess interval. This general approach has desirable characteristics ina frequency hopping system, as the propagation characteristics betweendevices may change significantly as the NET changes from frequency tofrequency within the hopping sequence, or over several Access Intervalsduring the dwell time on a single frequency. Reduction in data rate inthis system is primarily intended to remedy the data smearing(inter-symbol interference) effects of dispersion due to excess delay,rather than temporary poor signal to noise ratio due to frequencyselective fading. Devices that receive high data is rate transmissionswith acceptable signal strength but high jitter are likely to beexperiencing the effect of dispersion.

The concept of allowing Polls and message fragments to occur at either ahigh or low data rate could create difficulties for other NETconstituents that need to be able to monitor the channel for reservationinformation. Two embodiments for solving this problem are the use ofauto-discriminating receivers or the use of fixed data rate headers forsystem communications.

Auto discrimination requires the receiver to process messages sent ateither data rate, without necessarily having prior knowledge of therate.

Given a high rate of 1 MBIT/SEC, and a low Rate of 250 KBPS, i.e., onebeing a binary multiple of the other, it is possible to devise preamblesthat can be received at either rate. Consider that 01 and 110 sent atthe low rate correspond to 00001111 and 111111110000 at the high rate.These preambles are transmitted continuously before the transmission ofthe High-Level Data Link Control FLAG character at the correct data rateindicating the start of a message. In this example, a preamble of 20bits of 01 at the low rate indicates operation at the high rate. Apreamble of 30 bits of 110 indicates operation at the low rate. Areceiver tuned to either rate is capable of receiving both types ofpreambles and initiating the proper decoding mechanisms for the intendedrate of transmission.

This general technique, with appropriate selection of preamble content,is applicable to binary modulation schemes, for example, a frequencymodulated system where a common frequency deviation value is used forboth data rates. It is also applicable to systems where switching occursbetween binary and multilevel modulation, such as disclosed in pendingU.S. application Ser. No. 07/910,865, filed Jul. 6, 1992.

Referring now to FIG. 25, a preamble 2501, a SYNC 2503 and a ReservationPoll 2505 is illustrated. The preamble 2501 starts at the beginning ofthe Access Interval 2500 and is applied to an RF modem while it isswitching frequencies. Since the switching time is a worst case, thiscauses the preamble 2501 to be present and detectable prior to theallocated 150 μsec period in some instances. It would be equallyappropriate to begin preamble transmission 50 or 100 μsec into theswitching period if that would be more convenient. The timing has beenselected to allow 100 μsec.

Referring to FIG. 26, a sample SYNC message 2600 is shown. Referring toFIG. 27, a sample Reservation Poll 2700 is shown. In these examples, thehopping synchronization information has been positioned in theReservation Poll 2700.

With auto-discrimination, it is possible to change data rates on aper-poll basis, thereby adjusting for channel temporal dynamics. Sinceall devices in the NET have auto discrimination capabilities, andchannel reservation information is included in message headers as alength field, the bandwidth reservation features of the NET arepreserved. The maximum fragment duration may be maintained at a fixedvalue, meaning that low data rate fragments convey less data than theirhigh rate counterparts, or may be scaled in the ratio of the data ratesto allow consistent fragment data payloads.

An alternative to auto-discrimination is the use of headers tocommunicate system information. This embodiment is less preferred, butmay be appropriate if economics, size, or power constraints dictate asimpler design than that required for auto-discrimination. In thisembodiment, any transmission at the lower data rate is preceded by aheader at the high data rate that conveys NET management information,i.e., channel reservation status. Devices other than those directlyinvolved in polling or fragment transmission need only monitor at thehigh rate for channel reservation information. The header at the highrate and the following transmission at the low rate are concatenatedHigh-Level Data Link Control frames, with an appropriate preamble forlow rate clock recovery synchronization in-between.

For the communicating devices, the header can serve the additionalpurpose of acting as a test pattern at the high rate. For example, if adevice is polled at the low rate, but successfully decodes the high rateheader with adequate signal quality, it may indicate back to the pollingunit to poll again at the high rate.

In a premises LAN as discussed in reference to FIG. 1, many NETs may bedistributed geographically to provide enhanced coverage or additionalsystem capacity. The wired portion of the network infrastructure, suchas Ethernet or Token Ring, provides a means for coordination of NETs toachieve optimum system performance. An equally important role of thewired infrastructure is to allow resource sharing. Portable devices withlimited memory capacities, processing power, and relatively smallbatteries may access large data bases on, or remotely initiateprocessing capabilities of, larger AC powered computer systems.Portable/mobile devices may also share communication with other likedevices which are serviced by other NETs well beyond the radio coveragerange of their own NET.

The basic method for communication of status information regarding thepremises LAN is the HELLO message. HELLO messages are sent routinely,but relatively infrequently, for example, every 90 Access Intervals. TheHELLO transmission interval is tied to the Priority SYNC interval, sothat the HELLO interval corresponds to Access Intervals where SYNC istransmitted if the network is lightly utilized.

In an alternate embodiment, HELLOs could be inserted as a broadcastmessage at the beginning of the Sessions period. FIG. 8 illustrates apreferred Access Interval embodiment where a HELLO message 801 isinserted between a SYNC 803 and a Reservation Poll 805. The SYNC frameat the beginning of the Access Interval indicates that the AccessInterval will contain a HELLO, allowing power managed devices to remainawake to receive the HELLO.

HELLO messages may also contain information regarding pending changes inthe local NET. If the local NET is changing Access Interval durations orhop sequences, for instance, changes may be communicated in severalconsecutive HELLOs so that the information is reliably communicated toall NET constituents, permitting all devices to make the change incoordinated fashion. Further discussion of HELLO message content isprovided below.

For purposes of channel management in the Access Interval structure, themaximum transmission duration by a device should be limited to the timethat the device moving at a maximum expected velocity can traverse ¼wavelength of the maximum carrier frequency. The duration may be furtherreduced to compensate for link bit error rate characteristics orexpected duration or frequency of interference bursts. A maximumtransmission duration of 2.5 ms is suitable for 1 MBIT/SEC transmission,with a device velocity of 15 mph, in a multiple NET environment.

Use of spatial or polarization antenna selection diversity is alsodesirable in indoor propagation environments. First, the receiving unitmakes an antenna diversity decision during the preamble portion of eachtransmission. The antenna used for reception for each device address isthen recorded in memory so that the correct antenna will be used forresponse messages to each address. While diversity selection is onlyvalid for a short time, it is not necessary to age this information,because antenna selection is equi-probable even after diversityinformation is no longer valid.

The Access Interval structure of the present invention also inherentlyprovides routine channel sounding for each hop. This is important in afrequency hopping system, as channel conditions will vary considerablyfrom frequency to frequency within the hopping sequence. NETconstituents must, in most cases, be able to receive SYNC andReservation Poll transmissions from the Control Point device to attemptinbound access in an Access Interval. This provides a positiveindication that the device is not experiencing a channel outage,allowing power saving and eliminating possible channel contention.Channel sounding does not need to be employed during periods where theNET is not busy since contention is unlikely in this situation.

Channel sounding for Outbound messages is accomplished through a Requestfor Poll/Poll cycle where handshaking messages with short time outperiods must be successfully communicated before longer messagetransmissions may be attempted.

As discussed above with regard to FIG. 1, a premises LAN consists ofseveral access points 15 located throughout an environment requiringwireless communications, e.g., a building or other facility, or a campuscomprised of several buildings. The access points 15 are placed toprovide coverage of intended usage areas for the roaming portable ormobile computing devices 20. Coverage areas must overlap to eliminatedead spots between coverage areas.

The access points 15 may be interconnected via industry standard wiredLANs, such as IEEE 802.3 Ethernet, or IEEE 802.5 Token Ring. Accesspoints may be added to an existing LAN without the need to installadditional LAN cable. Alternatively, it may be desirable to installaccess points on dedicated LAN segments to maximize performance of boththe radio network and other collocated computer devices.

Access points within the premises LAN provide Control Point functionsfor individual NETs. NETs employ different hopping sequences to minimizepotential interference between NETs. Regulatory restrictions generallypreclude synchronization of multiple NETs to a single master clock,requiring that individual NETs operate independently from one another.The lack of the ability to coordinate timing or frequency usage betweenNETs introduces the potential for collisions between independent NETswith overlapping coverage areas.

FIGS. 9 a and b illustrate conceptually how multiple NETs may beemployed in an idealized “cellular” type installation. Each hexagon 901and 903 in FIG. 9 a represents the primary coverage area of a given NET.Coverage areas are modeled as circles 905 based upon some reliabilitycriterion, for example a 5% mean fragment retry rate (on average 95% offragments are successfully communicated on the first attempt). Typicalcoverage areas are determined by physical attributes of the area inwhich the NET operates. As is illustrated in FIG. FIG. b for the hexagon(NET) 903 of FIG. 9 a, an actual coverage area 907 meeting thereliability criterion is likely to be irregular. This may require accesspoints to be offset significantly from the hexagonal grid.

FIG. 10 illustrates a coverage contour overlap for the multiple NETs inthe premises LAN of FIG. 1. Darken shaded areas 1001 indicate areaswhere access point coverage overlaps. Because the coverage distance of aradio system on an instantaneous basis greatly exceeds the coverage thatcan be provided on average to sustain a given quality of service, theoverlap at any instant may be significantly greater than the coveragecontours indicate.

FIG. 11 illustrates hopping sequence reuse in a multiple NETconfiguration. Hopping sequence re-use may be necessary if there arephysical constraints on the number of hopping sequences that can besupported. For example, devices may have limited memory available forhopping sequence storage. Use of a smaller set of sequences alsosimplifies the task of determining sets of sequences that haveacceptable cross correlation properties. In FIG. 12, 7 hopping sequences1 through 7 are used throughout the coverage area. Other NETs may reusethe same hopping sequence at some distance removed. While 7 NETs areillustrated, larger numbers, such as 9 or 15 may provide a bettercompromise between minimizing the number of hopping sequences used, andreuse distance between NETs using the same sequence. Reuse requirescoordination of hopping sequence assignment—either the system installercan coordinate the installation, or the system may include automatedmanagement features to assign hopping sequences to individual NETs.

Since NETs are not synchronized, different NETs that use the samehopping sequence are likely to interfere during periods where oscillatordrift causes them to be temporarily synchronized. At other times, theymay only interfere due to imperfect channelization. For example, for aworst case 100 ppm frequency error between two NETs using the same 79frequency sequence at one Access Interval per hop and 50 hops persecond, NETs will partially or fully overlap for a duration of 10minutes every 4.3 hours. Typically the frequency error will be 25% to50% of the worst case, leading to longer overlap periods occurring lessfrequently.

NETs using the same hopping sequence must be physically isolated fromone another to reduce interference to an acceptable level. Extensivehopping sequence reuse generally requires site engineering andoptimization of access point placement. Using more hopping sequencesreduces the need for critical system engineering during installation.Fifteen hopping sequences is a preferred number for hopping sequencereuse, allowing simplified installation and minimal coordination.

NETs that use different hopping sequences will also temporarilysynchronize in timing relationships that cause mutual co-channelinterference on common channel frequencies. Since the number of channelsthat must be used in a sequence is a significant fraction of the totalnumber of channels available, all sequences will share some number offrequencies in common. When sequences are time aligned so that a commonfrequency is used simultaneously, interference can occur. Optimizationof sets of sequences for low cross correlation is necessary to preventvarious time alignments of sequences from having more than one or twofrequencies in common.

Optimization of hopping sequences for multiple NETs must also includeanalysis of imperfect channelization. The performance characteristics ofthe RF modems may not, for economic or power consumption reasons,provide sufficient transmitter spectral containment, receiver dynamicrange, or receiver selectivity to guarantee that devices operating ondifferent frequencies in proximity to one another will not interfere. Inselecting hopping sequences for desirable cross correlation properties,adjacent and alternate adjacent channel interference must be considered.Protocol retry mechanisms for fragments lost to adjacent channelinterference or limited dynamic range may be randomized to preventcontinued disruption of communications in the affected NET.

Often in campus environments where systems must provide coverage inseveral buildings, the cost of wiring LAN cable between access points isprohibitive. To establish connectivity between access points in anpremises LAN, it may be necessary to provide wireless links betweengroups of access points connected to separate LAN segments. FIG. 12illustrates a wireless link 1201 connecting groups of access points 1203and 1205. The access points 1203 and 1205 are connected on separate LANsegments 1207 and 1209.

In one embodiment, the access points 1203 and 1205 may be configured ina wireless point to point mode, wherein one access point serves as acontrol point device while the others operate in a slaved mode dedicatedto point to point data transfer. Slave access points are configured tooperate as portable/mobile devices, and forward communications to masterbases by sending Request for Polls during reservation opportunities orImplicit Idle Sense periods. Because of the potential high traffic ofpoint to point links, separate NETs may be allocated for this purpose,with a master communicating with one or more slave units. Master unitsmay also communicate with other portable/mobile devices. The COSTweighing (discussed below) in a slave's HELLO transmission is preferablyset to a high value, to force portable/mobile devices which can connectto another NET to do so.

In another embodiment, it may also be desirable to support wirelessaccess points. Wireless access points serve as control points, but arenot connected to the infrastructure through a LAN cable. As isillustrated in FIG. 13, a wireless access point 1301 participates in thepremises LAN through a wireless link 1303 to an access point 1305 thatis connected to a LAN 1307.

Wireless access points operate as slave devices to master access pointswhich are connected to the wired infrastructure. The wired and wirelessaccess points share the same hopping sequence, and are synchronized as acommon NET. Because they are not connected to the Infrastructure,wireless access points must be used as store and forward devices. Eachtransmission to a wireless base must be retransmitted to the intendeddestination device, doubling the number of transmissions occurring inthe NET. Wireless access points are preferably used for supplementingcoverage area of the premises LAN. For example, a wireless access pointmight provide spot coverage of isolated “dead spots” where data trafficis limited or where providing a wired LAN connection is difficult.Wireless access points may also serve as emergency spares to providecoverage in the event of a failure of a primary access point. In thisrole, the wireless access point may be either permanently installed inselected locations, or stored in a maintenance area and quicklypositioned and connected to AC or battery power to providecommunications while repairs are made to the primary wired access point.Moreover, permanently installed wireless access points might also beused for redundancy, i.e., to monitor an associated access point and totake over when a break-down is detected.

The preferred wireless access point embodiment uses interleaved accessintervals. The parent wired access point and secondary wireless accesspoint coordinate Access Intervals, the wired access point deferringevery third or sixth access interval to the wireless base. Since thewired access point transmits priority SYNC messages every third AccessInterval, the wireless access point may routinely be allocated one ofthe two intervening Access Intervals for priority SYNC communicationswith devices that are attached to it. Communication between the wiredand wireless access points may occur during Access Intervals initiatedby either access point. Wireless access points may also communicate withdevices during an Access Interval using Implicit or Explicit Idle Sense.

This embodiment provides predictable access for devices attached to thewireless NET, and allows the same power management algorithms to be usedregardless of whether the access point is wired or wireless. Thewireless access point may transmit its own priority SYNC and HELLOmessages. Also, devices seeking communications with the wireless accesspoint will automatically be synchronized with the wired base as well,allowing immediate improved access to the network if their mobility hasput them within range of the wired base.

Because of the constraint of sharing bandwidth with a wired accesspoint, connectivity of wireless access points is normally limited to oneper wired access point. However, in cases where system loading ispredictably and consistently light, multiple wireless access pointscould share a single wired base, e.g., each transmitting in turn in theAccess Intervals between the Wired Base Priority SYNC Access Intervals.

Wireless access points are capable of supporting scheduled traffic.However, since each transmission to a wireless access point must beforwarded, scheduled transmissions through wireless access points usetwice the bandwidth as those through wired access points. In otherwords, twice the number of Time Division Multiple Access slots must beallocated. To avoid introducing excessive delay, communications must beforwarded during the same Access Interval that they are received, orshorter Access Intervals must be used. Scheduled traffic slotassignments must be common to all wireless bases operating within asingle NET.

Wireless access points require reliable communication with their wiredcounterparts. This dictates smaller coverage contours for wirelessaccess points. If a wired access point provides 80,000 square feet ofcoverage area, a wireless base can be predicted to provide only anadditional forty percent coverage improvement, due to overlap with thewired access point. Frequently, access points are mounted at ceilinglevel, providing a relatively clearer transmission path between accesspoints than exists between bases and portable/mobile devices located inmore obstructed areas near the floor. With careful site engineering andinstallation, a wireless access point can provide somewhat better thanthe forty percent predicted improvement, but still less than thecoverage of an additional wired base.

As discussed above, HELLO messages are used to communicate NET andpremises LAN status messages. They facilitate load leveling and roamingwithin the premises LAN and allow sequence maintenance to improvesecurity and performance within the NET. HELLO messages occurperiodically in Access Intervals that contain priority SYNC messages.HELLOs are sent periodically relative to the sequence length, forinstance, every 90 Access Intervals. HELLOs, like SYNC information, areoptionally encrypted to provide greater security.

Each HELLO message includes a field for COST. COST is a measure of theaccess point to handle additional traffic. A device determining which oftwo or more access points having adequate signal strength to registerwhich will select the base with the lowest COST factor.

The base computes COST on the basis of how many devices are attached tothe NET, the degree of bandwidth utilization, whether the base is wiredor wireless, the number of frequencies experiencing consistentinterference within the sequence, and the quality of the connection thebase has within the premises LAN.

FIG. 14 illustrates the concept of access points communicatingneighboring access point information through HELLO messages tofacilitate roaming of portable/mobile devices. In a premises LAN, accesspoints 1401, 1403 and 1405 communicate SYNC information amongstthemselves via wired backbone (LAN) 1407. In addition, a wireless accesspoint 1409 (discussed above) similarly communicates with the accesspoints 1401, 1403 and 1405 via a wireless link 1411. A portable/mobiledevice 1413 is initially registered with access point 1401, which actsas a control point for the portable/mobile device 1413. HELLO messagestransmitted by access point 1401 to portable/mobile device 1413 containfields for neighboring access points 1403, 1405 and 1409. These fieldsmay indicate, for example, addresses of the neighboring bases, theirCOST, the hopping sequences, hopping sequence indices, number of AccessIntervals per hop, and NET clock. The portable/mobile device 1413detects the HELLOs transmitted from access point 1401 and uses theinformation for coarse synchronization with the other access points1403, 1405 and 1409. This permits the portable/mobile device to roambetween access point coverage areas (i.e., between different NETs)without going through a full acquisition phase. Roaming ofportable/mobile devices is discussed in more detail below.

Simply put, communication of neighbors' information permits each accesspoint to advise its associated portable/mobile devices (i.e., thosehaving common communication parameters) on how to capture HELLO messagesfrom neighboring access points having different communicationparameters. Such communication parameters may include, for example,hopping sequences, spreading codes, or channel frequencies.

For example, neighbors' information transmission is appropriate in anycase where the system uses more than a single channel. For instance, ina direct sequence architecture, a single spreading code is often used.Capacity can be added to such a network by employing different spreadingcodes at each access point. The neighbors' information included in theHELLO message from a given access point would include the spreadingsequences of access points providing coverage in adjacent coverageareas. Likewise, in a multiple frequency channelized system, HELLOmessages would include the channel frequencies of adjacent accesspoints.

In addition to facilitating roaming, communication of neighbors'information may also facilitate the initial selection of an access pointby a portable/mobile device attaching to the premises LAN for the firsttime.

Access point HELLO messages may also facilitate adaptive access pointtransmitter power control. For example, each access point HELLOtransmission could specify the transmitter power level being used by theaccess point. If a given attached portable/mobile device notes that thecurrent access point transmitter power level is unnecessarily high(creating the possibility of interference with other access points), theportable/mobile unit could send a message to the access point indicatingas such, and the access point could adjust the transmitter power levelaccordingly.

HELLO messages also enable communication of information indicating toall devices that certain changes in the NET are required. For example,the NET may switch hopping sequences periodically to improve security,or to avoid interference sources that consistently interfere with one ortwo frequencies within a given sequence. Interference may result fromoutside sources, or from other NETS. Changes to the NET are communicatedover the course of several HELLO messages (with a countdown) before thechange occurs, so that all devices are likely to be aware of changes andsynchronize at the instant of change.

In addition, if encryption is used, the encryption key may beperiodically changed in HELLOs. Like hopping sequence changes, KEYchanges are sent over several HELLOs, and are encrypted using theexisting key until the change goes into effect.

As mentioned above, roaming portable and mobile computing devicesoperating in the premises LAN will routinely move between access pointcoverage areas. At the maximum device velocity and expected coveragearea per access point, a mobile device may be expected to cross a NETcoverage contour in several seconds. Because of the use of multiple,non-synchronized frequency hopping NETs, it is more difficult to providefor simple hand-off between access points than it would be in a systemthat used cellular techniques with a single frequency per cell. Thepremises LAN makes special provisions for roaming by transmitting coarsefrequency hopping synchronization information in HELLO messages.

The premises LAN uses a spanning tree algorithm to maintain currentinformation regarding the general location of mobile devices within thenetwork. When a device changes registration from one NET Control Pointto another, routing information is updated throughout theinfrastructure. Wired access points may broadcast spanning tree updatesto attached wireless access points.

In the premises LAN, roaming portable and mobile devices initiallyselect and register with an access point Control Point on the basis oflink quality, i.e., signal quality, signal strength and COST informationtransmitted within HELLO messages. A device will remain attached to aparticular access point until the link quality degrades below anacceptable level, then it will attempt to determine if an alternativeNET is available. Different device operating scenarios dictate differentroaming strategies, discussed below.

An idle device monitors SYNC and HELLO messages from the Control Pointdevice to maintain NET connectivity. Type is 2 devices do not employpower management, and always maintain their receivers in an activestate. They monitor all SYNC messages. Type 1 and Type 3 devicestypically employ power management, operating in standby or sleep modesof operation for many Access Intervals before activating their receiversfor monitoring SYNC and HELLO messages. Control Points are guaranteed tosend Priority SYNC frames every third Access Interval. HELLOs occurevery 30th Priority SYNC frame. Power managed devices employ sleepalgorithms synchronized to wake for the minimum period necessary toguarantee receipt of priority SYNC, HELLO, and Pending Messagetransmissions before resuming SLEEP.

Type 2 devices are typically operated from high capacity vehicular powersystems, which eliminates the need for power management. These devicesmay travel at velocities near the maximum system design specification,dictating more frequent roaming. Type 2 devices will initiate a searchfor an alternative NET if SYNC messages are consistently received atsignal strengths below a Roaming Threshold or if reception errors areconsistently detected. Because of the effects of frequency selectivefading, signal strength information is averaged over the course ofseveral hops within the hopping sequence.

If roaming is indicated, the device initiates a Roaming Algorithm, usingNeighbors' information from the most recent HELLO to attemptsynchronization with another candidate NET. If SYNC is not detectedwithin 6 hops, another candidate from the Neighbors list will beselected, and the process repeated. Once SYNC is attained on analternative NET, the device will monitor signal strength and data errorsfor several hops to determine link quality. If link quality isacceptable, the device will continue monitoring until a HELLO isreceived. If COST is acceptable, it will then register with the new NET.The Control Point device will update the spanning tree over the wiredbackbone (or by RF if a wireless base). If link quality or COST isunacceptable, another candidate from the Neighbors list is selected andthe process repeated. This continues until an acceptable connection isestablished. If a connection cannot be established, the device mustreturn to the original NET or employ the initial acquisition algorithm.

Type 2 devices also have the option of monitoring other NETs beforedegradation of their NET connection. They may do so by monitoring theirown NET for the SYNC and pending message list transmissions, thenscanning other candidate NETs during the Sessions period of their NET.Other type devices may do so less frequently.

Type 1 and Type 3 devices may sleep extensively when idle, preferablyactivating every nine Access Intervals to resynchronize and checkpending messages. Successful reception of at least one SYNC during threemonitoring periods is necessary to maintain fine synchronization to theNET clock. Failure to receive two of three SYNC frames, or receipt oftwo or three SYNC messages with poor signal strength are possibleindications of the need to further test link quality by remaining activefor several consecutive SYNC transmissions. If signal strength or dataerrors over several hops indicates that link quality is poor, or if areceived HELLO message indicates high COST, the roaming algorithm isinitiated, and alternative NETs are evaluated, as in the case of Type 2devices.

Some battery powered devices may sleep for periods of time more thannine Access Intervals. For example, devices with extremely limitedbattery capacity may sleep between HELLOs, or several HELLO periods,after which they must remain active for several consecutive AccessIntervals to regain fine synchronization and assess whether to initiateroaming.

A Type 1, Type 2, or Type 3 device that has inbound message requirementsimmediately activates its receiver and waits for a SYNC and subsequentReservation Opportunities.

A device that does not detect SYNC messages over the course of sixAccess Intervals immediately initiates the Roaming Algorithm.

Outbound messages for devices that have changed coverage areas, butwhich have not yet registered with a new Control Point device, areproblematic. For example, in the premises LAN, messages will beforwarded to the access point that the device had previously beenattached to. The access point may attempt to poll the device during oneor more Access Intervals, then transmit the unit address in the pendingmessage list periodically for several seconds before disregarding it.Once the unit attaches to a base, the message must be transferred fromthe previous access point for delivery to the unit. All of theseactivities require transmission bandwidth on either the backbone or RFmedia, waste processing resources within the premise LAN, and result indelayed delivery.

As this premises LAN embodiment is designed, the network has no means ofdistinguishing messages it cannot deliver due to roaming from messagesthat should be retried due to signal propagation characteristics,interference, or sleeping devices. For this reason, the roamingalgorithm may be designed to allow devices to quickly detect that theyhave lost connectivity within their current NET, and re-attach to a morefavorably located access point.

Some improvement in delivering pending messages to roaming terminals canbe obtained by routinely propagating pending message lists over thewired backbone. When a device attaches to an access point, that base isable to immediately ascertain that the device has a pending message, andinitiate forwarding of the message for delivery to the device.

In the preferred frequency hopping embodiment of the present invention,the hopping sequence consists of 3m±1 frequencies, where m is aninteger. 79 frequencies are preferred. This embodiment will supporthopping rates of 100, 50 hops per second at 1 Access Interval per dwell,25 hops per second at 2 frames per dwell, and 12.5 hops per second at 4frames per dwell. Other rates can be supported for other Access IntervalDurations. For example, if the Access Interval is optimized to 25 ms,hop rates of 80, 40, 20, and 10 hops per second would be supported.

All devices within the NET may have one or more hopping tables thatcontain potential hopping sequences that may be used. Up to 64 sequencesmay be stored in each device. Each sequence has an identifier, and eachfrequency in each sequence has an index. The sequence identifier andindex are communicated in the SYNC transmission.

All SYNC transmissions may be block encrypted to prevent unauthorizeddevices from readily acquiring hopping synchronization information. Tofacilitate encryption, the encryption key may initially be factory setto a universal value in all devices. Users would then have the option ofchanging this key, by providing a new key to each device in the system.This may be accomplished through keyboard entry or other secure means.Keys may also be changed through the NET.

To facilitate hopping management, a hopping control portion of aprotocol controller will download a hopping table to a radio modem, andwill signal the radio modem when to hop. This approach consolidatestiming functions in the protocol controller, while not requiring thecontroller to be concerned with conveying frequency selection data tothe modem each hop.

The NET may switch hopping sequences periodically to improve security,or to avoid interference sources that consistently interfere with one ortwo frequencies within a given sequence. As mentioned above, changes tothe NET are communicated over the course of several HELLO messagesbefore the change occurs so that all devices are likely to be aware ofchanges.

Initial synchronization requires devices to ascertain the hoppingsequence, the hop rate, and the specific frequency from the hoppingsequence currently in use. Synchronization information is contained intwo types of routine messages. The SYNC field at the beginning of anAccess Interval contains synchronization information including thehopping sequence, the index of the current frequency within thesequence, the number of Access Intervals per hop, and the length of theAccess Interval. It also contains a timing character that communicatesthe NET master clock to all listening devices. Termination messages inthe Sessions period, ACK and CLEAR, contain the same information, but donot contain the timing character.

The simplest method for attaining synchronization is to Camp—select aquiet frequency that is likely to be within a sequence in use—and listenfor valid synchronization information. If a SYNC message is detected,the listening device immediately has both coarse and finesynchronization, and can begin the registration process.

If SYNC is not detected, but a termination message is, then the devicehas acquired coarse synchronization. The particulars of the hoppingsequence are known, but the boundaries of the dwells are not. To acquirefine synchronization, it begins hopping at the indicated hopping rate,listening for SYNC. If SYNC is not detected after a reasonable number ofhops, preferably 12 or 15, the device reverts to camping.

The worst case scenario for synchronization is to synchronize to asingle NET that is idle. Given a 79 frequency hopping sequence, oneAccess Interval per hop, and SYNC transmissions every third AccessInterval if the NET is idle, it may take nine cycle times to guaranteethat a SYNC transmission will be detected with 99.5% probability. At 50hops per second, synchronization could require as long as 14 seconds. At100 hops per second, 7 seconds is required.

At 2 Access Intervals per hop, a SYNC transmission is guaranteed tooccur every frequency over 2 cycles of the hopping sequence. Six cyclesare required for 99.5% probability of acquisition, corresponding to 19seconds at 25 hops per second.

At 4 Access Intervals per hop, at least one SYNC is guaranteed to occureach hop. Three cycles of the hopping sequence are required for 99.5%acquisition probability. At 12.5 hops per second, this also requires 19seconds.

This illustrates the advantage of scalability. A device that uses anacquisition algorithm suitable for 2 or 4 Access Intervals per hop willalso acquire a NET that hops at 1 Access Interval per hop. The algorithmmay be as follows:

-   -   1. The device scans candidate frequencies until it finds one        with no Received Signal Strength Indicator indication.    -   2. The device remains on the frequency for 6.32 seconds 2 Access        Interval/hop@25 Hops/second×2, or 4 Access Interval/hop@12.5        hops/second×1, or until it detects a SYNC message or a valid        termination message.    -   3. If SYNC is detected, the device synchronizes its internal        clock to the SYNC, and begins hopping with the NET for the next        11 hops. It may attempt registration after detecting valid SYNC        and any Reservation Opportunity. If synchronization is not        verified by detection of SYNC within the 11 hops, the        acquisition algorithm is reinitialized.    -   4. If a message termination (either an ACK or CLEAR) is        detected, the device immediately hops to the next frequency in        the sequence and waits for the SYNC. It is coarsely synchronized        to the NET but has a timing offset from the NET clock.

When the next SYNC is received, the device synchronizes its clock to theNET clock and initiates registration. If SYNC is not received within adwell time, the device hops to the next frequency in sequence. Thiscontinues until SYNC is attained, or until 15 hops have passed withoutreceiving SYNC, after which the acquisition sequence is restarted.

-   -   5. If coarse acquisition is not obtained within 6.3 seconds, the        device selects another frequency and repeats the process        beginning with step 2.

Camping provides a worst case acquisition performance that isperceptibly slow to the human user of a portable device. The preferredapproach has the receiver scan all potential frequencies in ascendingorder, at 125 μsec increments. When the highest frequency is reached,the search begins again at the lowest frequency. The 125 μs samplingrate is much faster than the 250 μsec channel switching timespecification of the RF modem. This is possible because the overallswitching time specification applies to worst case frequency switchingintervals, i.e., from the highest to the lowest operating frequency. Byswitching a single channel at a time, switching may be maintained overfrequency intervals very near a synthesizer phase detectors' phase lockrange, allowing nearly instantaneous frequency switching. The changefrom highest to lowest frequency at the end of the scan requires thestandard 250 μsec.

The 125 μsec monitoring interval allows 85 μs to ascertain if receiveclock has been detected prior to switching to the next frequency. Themonitoring interval should be selected to be non-periodic with respectto the access interval. For example, the 125 μsec interval allows theentire hopping sequence to be scanned 2(n+1) times in a 20 ms accessinterval.

If clock is recovered at any frequency, the receiver remains onfrequency for a Reservation Opportunity and initiates channel accessthrough the procedure described above. The scanning approach is lessdeterministic in terms of acquisition probability than camping, but thesearch time required for 99.5% acquisition probability is about 80Access Intervals, or three times faster than that for camping.

A hybrid approach that scans only three or four consecutive frequenciesincorporates the deterministic aspects of camping with some of theimproved performance of the scanning algorithm. For scanning over asmall number of frequencies an up/down scan is preferred, i.e.,1,2,3,2,1,2,3 since all frequency changes can be accomplished at thefaster switching rate. The end frequencies are visited less often thanthose in the center. The number of frequencies used, e.g., 3 or 4, isselected so that all can be scanned during the preamble duration of aminimum length transmission.

All devices are required to have unique 48 bit global addresses. Local16 bit addresses will be assigned for reduced overhead incommunications. Local addresses will not be assigned to devices whoseglobal addresses are not on an authentication list maintained in eachaccess point and routinely updated over the infrastructure.

Once a device has attained synchronization, it must register with thecontrol point to be connected with the NET. It initiates this by sendinga Request for Poll indicating a registration request, and including itsglobal address. The control point will register the device, and providea short. Network Address as an outbound message. The Control point willgenerate the short address if it is a single NET, or exchange the globaladdress for a short Network Address with a Network Address Server if theNET is part of a larger infrastructured network of a premises LAN.

Once a device is synchronized to a NET, it must periodically update itslocal clock to the NET clock communicated in the SYNC message. The SYNCmessage contains a character designated as the SYNC character thattransfers the NET clock synchronization. This may be the beginning orending FLAG in the SYNC message, or a specific character within themessage.

The maximum expected frequency error between NET and device local clocksis 100 parts per million. To maintain a 50 μs maximum clock error, thelocal device clock must be re-synchronized at 500 ms intervals. At 20 msper access interval, a non-sleeping device has up to 26 SYNCopportunities within that period in which to re-synchronize and maintainrequired accuracy.

As mentioned above, it is desirable that battery powered devices havethe capability to sleep, or power off, for extended periods of time toconserve power. The term sleeping terminal in this instance may refer toa device that powers down its radio communication hardware to save powerwhile maintaining other functions in an operational state, or a devicethat power manages those functions as well. In the power managed state,the device must maintain its hop clock so that full acquisition is notrequired every time power management is invoked.

Devices that must sleep to manage their power consumption use PrioritySYNC Messages to maintain synchronization. Priority SYNC Messages occurevery three Access Intervals. In times of low NET activity, non-prioritySYNC messages are omitted. By coordinating power management withPriority SYNC Messages, power managed devices can be guaranteed to wakeup for Access Intervals where SYNCs will be present, even if the NETactivity is low during the sleep period.

A sleeping device with no transmission requirements may sleep for eight20 ms access intervals, and wake only for the SYNC and Reservation Pollat the beginning of the ninth Access Interval to monitor pendingmessages before returning to the sleep state, for a duty cycle of lessthan 5%. This provides three opportunities to synchronize to the NETclock within a 540 ms window. A flow chart depicting the a devicesleeping for several access intervals is shown in FIG. 17.

Devices may also sleep for longer periods of time, at the risk of losingfine synchronization. They may compensate by advancing their localclocks to account for the maximum timing uncertainty. For example, aterminal could sleep for 5 seconds without re-synchronizing by waking up500 microseconds before it expects an Access Interval to begin, andsuccessfully receive SYNC messages. This technique is valid for extendedperiods of time, up to the point where the maximum timing errorapproaches 50% of an Access Interval. A flow chart depicting the adevice sleeping for several seconds is shown in FIG. 18.

A power managed device that requires communication during a sleep periodmay immediately wake and attempt access to the NET at the next availableReservation Opportunity.

A device requiring communications may be able to register with one ofseveral NETs operating in its vicinity, with transmissions occurring onmany frequencies simultaneously. A good strategy is to synchronize to aNET that provides an acceptable communication link, then monitor HELLOmessages to determine other candidate NETs before attaching to aparticular NET by registering with the control point device.

As described above, a spontaneous wireless local area network orspontaneous LAN is one that is established for a limited time for aspecific purpose, and which does not use the premises LAN to facilitatecommunications between devices or provide access to outside resources.Use of spontaneous LAN allows portable devices to share information,files, data, etc., in environments where communication via the premisesLAN is not economically justifiable or physically possible. Aspontaneous LAN capability also allows portable/mobile devices to havean equally portable network. Peripheral and vehicular LANs are examplesof such spontaneous LANs.

Requirements for spontaneous LAN differ from an infrastructured premisesLAN in several significant areas. The number of devices in a spontaneousLAN is likely to be smaller than the number that a single NET in apremises LAN must be capable of supporting. In addition, coverage areasfor spontaneous LANs are typically smaller than coverage areas for anaccess point participating in the premises LAN. In a spontaneous LAN,communication often takes place over relatively short distances, wheredevices are within line of sight of each other.

In an premises LAN, the majority of communications are likely to involveaccessing communication network resources. For example, portable deviceswith limited processing capabilities, memory, and power supplies areable to access large databases or powerful computing engines connectedto the AC power grid. Access points within the premises LAN are wellsuited to the role of Control Points for managing synchronization andmedia access within each NET.

In a spontaneous LAN, however, communications are limited to exchangeswith spontaneous NET constituents. Additionally, NET constituents maypotentially leave at any time, making it difficult to assign controlpoint responsibilities to a single device. A shared mechanism forsynchronization and media access is preferable in most cases.

In a spontaneous LAN, battery power limitations may preclude assignmentof a single device as a control point. The routine transmission of SYNCand access control messages places a significant power drain on aportable, battery powered device. Also, the control point architecturedictates that transmissions intended for devices other than the controlpoint be stored and forwarded to the destination device, furtherincreasing battery drain, and reducing system throughput.

Moreover, the use of scheduled transmission in a premises LAN is likelyto differ from use in a spontaneous LAN. For example, unlike thepremises LAN, in the spontaneous LAN, applications such as massaging andtwo way a voice communications may only occasionally be used, whereasvideo transmission and telemetry exchange may be prevalent.

To promote compatibility and integration with the premises LAN,operational differences required by multiple participating devicesshould be minimized. For example, selecting relatively close frequencybands for each LAN aids in the design of a multiple LAN transceiver,reducing circuitry, cost, power, weight and size while increasingreliability. Similarly, selecting communication protocols so that thespontaneous LAN protocol constitutes a subset or superset of premisesLAN may enable a given device to more effectively communication in bothLANs, while minimizing both the overall protocol complexity andpotentially limited memory and processing power.

Use of frequency hopping is desirable in premises LAN because of itsability to mitigate the effects of interference and frequency selectivefading. In the case of the latter, frequency hopping allows systems tobe installed with less fade margin than single frequency systems withotherwise identical radio modem characteristics, providing improvedcoverage.

The potentially smaller coverage area requirement of spontaneous LANs,however, allows single frequency operation to be considered for someapplications, e.g., such as a peripheral LAN. Regulatory structures arein place in some countries to allow single frequency operation in thesame bands as frequency hopping systems, providing that single frequencydevices operate at reduced power levels. The lower transmit power ofsingle frequency operation and elimination of periodic channel switchingare desirable methods of reducing battery drain. The choice of singlefrequency or frequency hopped operation is dictated by the coveragerequirements of the network, and may be left as an option to deviceusers.

As noted earlier, the basic Access Interval structure is suited tosingle frequency operation as well as to frequency hopping. SYNCmessages in a single frequency system substitute a single frequencyindication in the hopping sequence identifier field.

A spontaneous LAN comes into existence when two or more devicesestablish communications, and ceases when its population falls to lessthan two. Before a spontaneous LAN can be established, at least twodevices must agree upon a set of operating parameters for the network.Such agreement may be pre-programmed else exchanged and acknowledgedprior to establishing the spontaneous LAN. Once the spontaneous LAN isestablished, other devices coming into the network must be able toobtain the operating parameters and acquire access.

More specifically, to establish a spontaneous LAN, a computing devicemust first identify at least one other network device with whichspontaneous LAN communication is desired. To identify another networkdevice, the computing device may play an active or passive role. In anactive role, the computing device periodically broadcasts a request toform spontaneous LAN with either a specific network device or, morelikely, with a specific type of network device. If a network devicefitting the description of the request happens to be in range or happensinto range and is available, it responds to the periodic requests tobind with the computing device, establishing the spontaneous LAN.Alternately, the network device may take a passive role in establishingthe spontaneous LAN. In a passive role, the computing device merelylistens for a request to form a spontaneous LAN transmitted by theappropriate network device. Once such a network device comes into range,the computing device responds to bind with the network device,establishing the spontaneous LAN.

The choice of whether a device should take a passive or active role is amatter of design choice. For example, in one embodiment where peripheraldevices have access to AC power, the roaming computer terminals take apassive role, while the peripheral devices take a more active role.Similarly, in another embodiment where a vehicle terminal has access toa relatively larger battery source, an active role is taken whenattempting to form a spontaneous LAN, i.e., a vehicular LAN, with ahand-held computing device.

Binding, a process carried out pursuant to a binding protocol stored ineach network device, may be a very simple process such as might existwhen creating a spontaneous LANs that operates on a single frequencychannel. Under such a scenario, a simple acknowledge handshake betweenthe computing terminal and the other network device may be sufficient toestablish a spontaneous LAN pursuant to commonly stored, pre-programmedoperating parameters. However, more complex binding schemes may also beimplemented so as to support correspondingly more complex spontaneousLANs as proves necessary. An example of a more complex binding scheme isdescribed below.

It is desirable in some large spontaneous LANs for one device to bedesignated as a fully functional control point, providing identical NEToperation to a single NET in the premises LAN. Providing that alldevices share a hopping table and encryption key, the designated devicewould initiate control point activities, and other devices wouldsynchronize to the designated unit. A device with greater batterycapacity, or one that can be temporarily connected to AC power is bestsuited to the dedicated control point function. This architecture isapplicable to Client-Server applications (where the server assumes thecontrol point function), or to other applications where a single deviceis the predominant source or destination of communications. A portabledevice used as a dedicated control point is required to have additionalprogramming and memory capacity to manage reservation based mediaaccess, pending message lists, and scheduled service slot allocations.

In embodiments where communication requirements of a spontaneous LAN arelargely peer to peer, there may be no overwhelming candidate for adedicated Control Point. Thus, in such cases, the Control Point functionis either distributed among some or all the devices within thespontaneous LAN. In such scenarios, the interleaved Access Intervalapproach used for wireless access points is employed. Initially, controlpoint responsibilities are determined during the binding process. Usersmay designate or redesignate a Control Point device when severalcandidates are available.

For spontaneous LANS, access intervals may be simplified to reduce powerconsumption, program storage and processing power requirements forportable devices used as control points. Control Point devices transmitSYNC, pending message lists, and Time Division Multiple Access slotreservations normally, but only use the single slot reservation Poll(Idle Sense Multiple Access). The reservation poll contains a fieldindicating reduced control point functionality. This places otherdevices in a point-to-point communication mode, using the Implicit IdleSense Algorithm. The probability factor p communicated in thereservation poll is used for the Implicit Idle Sense algorithm. Controlpoint devices may use the deferred SYNC mechanism for light systemloading, transmitting Priority SYNC every third Access Interval tofurther decrease their transmission requirements. Control point devicesmust monitor the reservation slot for messages addressed to them, butmay sleep afterwards.

Request for Polls initiated under Implicit Idle Sense use point-to-pointaddressing, indicating the address of the destination device directly,rather than the control point device. This eliminates the need for theControl Point device to store and forward transmissions within thespontaneous LAN. The device detecting its address in a Request for Pollbegins a session, after employing the Implicit Idle Sense algorithm, byPolling the source address identified in the Request for Poll. Theterminating ACK and CLEAR messages contain an Explicit Idle Senseprobability factor equal to that in the original reservation poll.

To allow for power managed devices, the Control Point device maintains apending message list. Devices that have been unable to establishcommunication with a sleeping device initiate a session with the ControlPoint device to register the pending message. Upon becoming active, thesleeping device will initiate a Poll to the device originating thepending message. The Control Point device will eliminate the pendingmessage indication by aging, or by receipt of communication from thedestination device clearing the pending message. Control point devicesare not required to store pending messages, only addresses. As mentionedabove, HELLO messages are broadcast to indicate changes in NETparameters. HELLO messages may be omitted to simplify the Control Pointfunction in spontaneous LANs.

Devices are assigned local addresses upon registration with the ControlPoint device. Devices may communicate an alias that identifies thedevice user to other users to the Control Point device where it isstored in an address table. The address table may be obtained by othernetwork constituents by querying the Control Point device. A peripheralLAN is a type of spontaneous LAN which serves as a short rangeinterconnect between a portable or mobile computing device (MCD) andperipheral devices.

Designers of portable products are constantly challenged with reducingsize, weight, and power consumption of these devices, while at the sametime increasing their functionality and improving user ergonomics.Functions that may be used infrequently, or which are too large to fitwithin the constraints of good ergonomic design may be provided inperipheral devices, including printers, measurement and dataacquisition-units, optical scanners, etc. When cabled or otherwisephysically connected to a portable product, these peripherals oftenencumber the user, preventing freedom of movement or mobility. Thisbecomes more problematic when use of more than one peripheral isrequired.

A second consideration for portable product design is communicationdocking. A communication dock is a device that holsters or houses aportable unit, and provides for communication interconnection for suchtasks as program downloading, data uploading, or communication withlarge printers, such as those used for printing full sized invoices invehicular applications. Communication docking of a portable unit mayalso involve power supply sharing and/or charging.

The requirement for communication docking capability forces newerportable product designs to be mechanically compatible with olderdocking schemes, or may require that new docks, or adapters, bedeveloped for each new generation of portable device. Product specificdocking approaches eliminate compatibility between devices manufacturedby different suppliers. This has hindered development of uniformstandards for Electronic Data Interchange between portable devices andfixed computing systems.

Physical connection between a portable device with a peripheral orcommunication dock also hinders user efficiency. Peripheral devices aregenerally attached with cable. If a peripheral is small enough to becarried or worn on a belt, the mobility of the user may be maintained.If a user must carry a hand-held portable device that is connected to abelt mounted peripheral the assembly cannot be set down while a taskthat requires movement to a location several feet away is undertakenunless the portable device and peripheral are disconnected. Likewise,connection to peripherals too large to be portable requires the user tofrequently connect and disconnect the device and the peripheral.

Use of wireless peripheral LAN interconnection greatly simplifies thetask of portable devices communicating with peripherals. In doing so,wireless connectivity allows improved ergonomics in portable productdesign, flexibility in interconnection to one or more peripherals,freedom of movement over a radius of operation, forward and backwardcompatibility between portable units and peripherals, and potentialcommunications among products manufactured by different vendors.

Constituents within a peripheral LAN generally number six or fewerdevices. One roaming computing device and one or two peripheralscomprise a typical configuration. Operating range is typically less thanfifty feet.

Because the computing devices generally control the operation ofperipheral devices, in a peripheral LAN a master/slave type protocol isappropriate. Moreover, roaming computing devices serving as master arewell suited to the role of Control Points for managing synchronizationand media access within each peripheral LAN. All peripheralcommunications are slaved to the master.

In a peripheral LAN, roaming mobile or portable computing devices andwireless peripherals may all operate from battery power. Operatingcycles between charging dictate use of power management techniques.

Although all participants in a peripheral LAN might also be configuredto directly participate in the premises LAN, the trade-offs in cost,power usage and added complexity often times weighs against suchconfiguration. Even so, participants within a peripheral LAN can beexpected to function in a hierarchical manner, through a multipleparticipating device, with the premises LAN. Thus, the use of a muchsimpler, lower-power transceiver and associated protocol may be used inthe peripheral LAN.

As previously described, a roaming computing device serving as a masterdevice may itself be simultaneously attempting to participate in othernetworks such as the premises or vehicular LANs. Considerable benefitsarise if the radio and processing hardware that supports operationwithin the wireless network can also support such operation. Forexample, a device that is capable of frequency hopping is inherentlysuited to single frequency operation. If it can adjust transmitter powerlevel and data rate to be compatible with the requirements of theperipherals LAN, it can function in both systems. The major benefits ofcommon transceiver hardware across LANs include smaller product size,improved ergonomics, and lower cost.

Specifically, in one embodiment, radio communication on the premisesLAN, as described herein, takes place using radio transceivers capableof performing frequency-hopping. To communicate on a peripheral LAN,such transceivers could also utilize frequency-hopping at a lower power.However, such transceivers are relatively expensive in comparison to alower power, narrow-band, single frequency transceivers. Because of thecost differential, it proves desirable to use the single frequencytransceivers for all peripheral devices which will not participate inthe premises LAN. Therefore, the more expensive, frequency-hoppingtransceivers which are fitted into roaming computing devices are furtherdesigned to stop hopping and lock into the frequency of the singlefrequency transceiver, allowing the establishment of peripheral LANs.

Instead of frequency hopping, the peripheral LAN may also usenarrow-band, single frequency communication, further simplifying theradio transceiver design for commonality. In another embodiment of theperipheral LAN transceivers, operation using one of a plurality ofsingle frequency channels is provided. Thus, to overcome interference onone channel, the transceiver might select from the remaining of theplurality an alternate, single operating frequency with lesser channelinterference. To accommodate the plurality of single frequency channels,the peripheral LAN transceivers may either communicate an upcomingfrequency change so that corresponding peripheral LAN participants canalso change frequency, or the transceivers may be configured to usefrequency synthesis techniques to determine which of the plurality acurrent transmission happens to be.

The Access Interval structure is also an appropriate choice forperipheral LAN operations. In one embodiment, to provide for simplicityand tighter integration, the Access Interval for the peripheral LAN is asubset of the Access Interval used in the premises LAN. HELLO messages,Implicit Idle Sense, Data Rate Switching, and scheduled services are notimplemented. Peripheral devices normally sleep, activate their receiversfor SYNC transmissions from the participating master device, and resumesleeping if no pending messages are indicated and they have no inboundtransmission requirements. Access Intervals occur at regular intervals,allowing for power management. Access Intervals may be skipped if themaster has other priority tasks to complete.

To initialize the peripheral LAN, a device desiring initialization, amaster device, selects a single operating frequency by scanning theavailable frequencies for one with no activity. A typical master devicemight be a roaming computing device desiring access to a localperipheral. Default values for other parameters, including AccessInterval duration, are contained within each participant's memory. Suchparameters may be pre-adjusted in each participant to yield specificperformance characteristics in the peripheral LAN.

Once a master device identifies a single frequency, slaves, which aregenerally peripherals, are brought into the peripheral LAN through aprocess called binding. Binding is initiated by the master device byinvoking a binding program contained therein. Slaves, such asperipherals, are generally programmed to enter a receptive state whenidle. Thus, in one embodiment, the master device accomplishes binding bytransmitting Access Intervals of known duration sequentially on a seriesof four frequencies spread throughout the available frequency range. Thespecific frequencies and Access Interval durations used are stored asparameters in all potential participating devices. A 250 KBPS transferrate is appropriate in some embodiments of the peripheral LAN,reflecting a balance between performance and complexity in peripheraldevices.

A slave, e.g., a peripheral, responds to the binding attempts by themaster device on a given frequency until the slave successfully receivesand establishes communication with the master device. If they do notestablish communication after four Access Intervals, the slave switchesto the next frequency for four Access Interval periods. Oncecommunication is established, the slave registers with the master andobtains the master device's selected operating frequency and relatedcommunication parameters. When all slave devices have been bound, themaster terminates the binding program and normal operation at theselected single frequency may begin.

Referring to FIG. 15, in a hierarchical network, peripheral LAN mastersuse a secondary access interval 1501 that is synchronized to the AccessInterval of a parent (premises) LAN control point. Peripheral LAN AccessIntervals occur less frequently than premises LAN Access Intervals,e.g., every other or every third Priority SYNC Access Interval.

During the premises LAN Access Interval, the peripheral LAN masterdevice monitors the premises LAN control point for SYNC 1503 reservationpoll 1505 and exchanges inbound and outbound message according to thenormal rules of the access protocol. The master switches to theperipheral LAN frequency, and transmits its own SYNC frame 1507 duringthe session period 1509 of its parent control point allowingcommunication with its peripherals. The peripheral LAN Access Intervalis generally shorter than the premises LAN Access Interval, so that itdoes not extend beyond the premises LAN Access Interval boundary. At theend of the peripheral LAN Access Interval 1501, the master switches tothe premises LAN frequency for the next SYNC 1503.

The secondary SYNC 1507 may only be transmitted if the peripheral LANmaster is not busy communicating through the premises LAN. If acommunication session is occurring, the master must defer SYNC,preventing communication with its peripherals during that AccessInterval. The master must also defer SYNC if the current frequency inthe LAN is prone to interference from the peripheral LAN frequency,i.e., they are the same frequency or adjacent frequencies. If twoconsecutive SYNCs are deferred, peripherals will activate theirreceivers continuously for a period of time, allowing the master totransmit during any Access Interval. This approach is also applicablewhen the master roams between frequency hopping NETs. Since NETs are notsynchronized to one another, the devices in the peripheral LAN adjustAccess Interval boundaries each time the master roams. If peripherals donot detect SYNC within a time-out period, they may duty cycle theirreception to conserve battery power.

Referring to FIG. 16, a Roaming Algorithm Flow Diagram illustrates how aroaming computing device will select a suitable access point. Roamingcomputing devices operating in the infrastructured network environmentformed by the access points will routinely move between access pointcoverage areas. The roaming computing devices are able to disconnectfrom their current access point communication link and reconnect acommunication link to a different access point, as necessitated bydevice roaming.

Access points transmit HELLO messages to devices in their coverage area.These HELLO messages communicate to roaming computing devices the costof connection through the access point, addresses of neighboring accesspoints, and the cost of connection through these neighboring accesspoints. This information allows roaming computing devices to determinethe lowest cost connection available and to connect to the access pointwith the lowest cost.

In addition, access point HELLO message may include communicationparameters of neighboring access points, such as frequency hoppingsequences and indices, spread spectrum spreading codes, or FM carrierchannel frequencies. This information allows roaming computing devicesto roam and change access point connections without going through a fullacquisition phase of the new access point's parameters.

Roaming computing devices initially select and register with an accesspoint control point on the basis of link quality: signal strength andcost information transmitted within HELLO messages. A device will remainattached to a particular access point until the link quality degradesbelow an acceptable level; then it will attempt to determine if analternative access point connection is available. The device initiates aroaming algorithm, using neighbors information from the most recentHELLO message to attempt connection with another candidate access point.If connection fails, another candidate from the neighbors list will beselected, and the process repeated. Once connection is made with analternative access point, the device will monitor signal strength anddata errors to determine link quality. If link quality is acceptable,the device will continue monitoring until a HELLO message is received.If the cost is acceptable, it will register with the new access point,and the access point will update the spanning tree over theinfrastructure. If link quality or cost is unacceptable, anothercandidate from the neighbors list is selected and the process repeated.This continues until an acceptable connection is established. If onecannot be established, the device must return to the original accesspoint connection or employ the initial acquisition algorithm.

FIG. 28 a illustrates an embodiment of the hierarchical communicationsystem according to the present invention communication is maintained ina warehouse environment. Specifically, a worker utilizes a roamingcomputing device, a computer terminal 3007, and a code reader 3009 tocollect data such as identifying numbers or codes on warehoused goods,such as the box 3010. As the numbers and codes are collected, they areforwarded through the network to a host computer 3011 for storage andcross-referencing. In addition, the host computer 3011 may, for example,forward cross-referenced information relating to the collected numbersor codes back through the network for display on the terminal 3007 orfor printing on a printer 3013. The host computer 3011 can be configuredas a file server to perform such functions. Similarly, the collectedinformation may be printed from the computer terminal 3007 directly onthe printer 3013. Other exemplary communication pathways supportedinclude message exchanges between the computer terminal 3007 and othercomputer terminals (not shown) or the host computer 3011.

The host computer 3011 provides the terminal 3007 with remote databasestorage, access and processing. However, the terminal 3007 also providesfor local processing within its architecture to minimize the need toaccess the remote host computer 3011. For example, the terminal 3007 maystore a local database for local processing. Similarly, the terminal3007 may run a variety of application programs which never, occasionallyor often need access to the remote host computer 3011.

Many of the devices found in the illustrative network are batterypowered and therefore must conservatively utilize their radiotransceivers. For example, the hand-held computer terminal 3007 receivesits power from either an enclosed battery or a forklift battery (notshown) via a communication dock within the forklift 3014. Similarly, thecode reader 3009 operates on portable battery power as may the printer3013. The arrangement of the communication network, communicationprotocols used, and data rate and power level adjustments help tooptimize battery conservation without substantially degrading networkperformance.

In the illustrated embodiment shown in FIG. 28 a, the hierarchicalcommunication system of the present invention consists of a premises LANcovering a building or group of buildings. The premises LAN in theillustrated embodiment includes a hard-wired backbone LAN 3019 andaccess points 3015 and 3017. A host computer 3011 and any othernon-mobile network device located in the vicinity of the backbone LAN3019 can be directly attached to the backbone LAN 3019. However, mobiledevices and remotely located devices must maintain connectivity to thebackbone LAN 3019 through either a single access point such as theaccess point 3015, or through a multi-hop network of access points suchas is illustrated by the access points 3015 and 3017. The access points3015 and 3017 contain a relatively higher power transmitter, and providecoverage over the entire warehouse floor. Although a single access pointmay be sufficient, if the warehouse is too large or contains interferingphysical barriers, the multi-hop plurality of access points 3017 may bedesirable. Otherwise, the backbone LAN 3019 must be extended to connectall of the access points 3017 directly to provide sufficient radiocoverage. Through the premises LAN, relatively stable, longer rangewireless and hard-wired communication is maintained.

Because roaming computing devices, such as the hand-held computerterminal 3007, cannot be directly hard-wired to the backbone LAN 3019,they are fitted with RF transceivers. To guarantee that such a networkdevice can directly communicate on the premises LAN with at least one ofthe access points 3015 and 3017, the fitted transceiver is selected toyield approximately the same transmission power as do the access points3015 and 3017. However, not all roaming network devices require a directRF link to the access points 3015 and 3017, and some may not require anylink at all. Instead, with such devices, communication exchange isgenerally localized to a small area and, as such, only requires the useof relatively lower power, short range transceivers. The devices whichparticipate in such localized, shorter range communication formspontaneous LANs.

For example, the desire by a roaming terminal to access peripheraldevices such as the printer 3013 and modem 3023, results in the roamingterminal establishing a peripheral LAN with the peripheral devices.Similarly, a peripheral LAN might be established when needed to maintainlocal communication between a code scanner 3009 and the terminal 3007.In an exemplary embodiment, the printer 3013 are located in a warehousedock with the sole assignment of printing out forms based on the codeinformation gathered from boxes delivered to the dock. In particular, assoon as the code reader gathers information, it relays the informationalong a peripheral LAN to the terminal 3007. Upon receipt, the terminal3007 communicates via the premises LAN to the host computer 3011 togather related information regarding a given box. Upon receipt of therelated information, the terminal 3007 determines that printing isdesired with the printer 3013 located at the dock. When the forklift3014 enters the vicinity of the dock, the terminal 3007 establishes aperipheral LAN with the printer 3013 which begins printing the collectedcode information.

To carry out the previous communication exchange, the printer 3013 andcode reader 3009 are fitted with a lower power peripheral LANtransceivers for short range communication. The computer terminal 3007transceiver is not only capable of peripheral LAN communication, butalso with the capability of maintaining premises LAN communication. Inan alternate exchange however, the code reader 3009 might be configuredto participate on both LANs, so that the code reader 3009 participatesin the premises LAN to request associated code information from the hostcomputer 3011. In such a configuration, either the code reader 3009 orterminal 3007 could act as the control point of the peripheral LAN.Alternately, both could share the task.

With capability to participate in the peripheral LAN only, the codereader 3009, or any other peripheral LAN participant, might still gainaccess to the premises LAN indirectly through the terminal 3007 actingas a relaying device. For example, to reach the host computer 3011, thecode reader 3609 first transmits to the computer terminal 3007 via theperipheral LAN. Upon receipt, the computer terminal 3007 relays thetransmission to one of the access points 3015 and 3017 for forwarding tothe host 3011. Communication from the host 3011 to the code reader 3009is accomplished via the same pathway.

It is also possible for any two devices with no access to the premisesLAN to communicate to each other. For example, the modem 3023 couldreceive data and directly transmit it for printing to the printer 3013via a peripheral LAN established between the two. Similarly, the codereader 3009 might choose to directly communicate code signals through aperipheral LAN to other network devices via the modem 3023.

In an alternate configuration, a peripheral LAN access point 3021 isprovided which may be directly connected to the backbone LAN 3019 (asshown), acting as a direct access point to the backbone LAN 3019, orindirectly connected via the access points 3015 and 3017. The peripheralLAN access point 3021 is positioned in the vicinity of other peripheralLAN devices and thereafter becomes a control point participant. Thus,peripheral LAN communication flowing to or from the premises LAN avoidshigh power radio transmissions altogether. However, it can beappreciated that a stationary peripheral LAN access point may not alwaysbe an option when all of the peripheral LAN participants are mobile. Insuch cases, a high power transmission to reach the premises LAN may berequired.

FIG. 28 b illustrates other features of the present invention in the useof spontaneous LANs in association with a vehicle which illustrate thecapability of automatically establishing a premises and a peripheral LANwhen moving in and out of range to perform services and report onservices rendered. In particular, like the forklift 3014 of FIG. 28 a, adelivery truck 3033 provides a focal point for a spontaneous LANutilization. Within the truck 3033, a storage terminal 3031 is docked soas to draw power from the truck 3033's battery supply. Similarly, acomputer terminal 3007 may either be docked or ported. Because ofgreater battery access, the storage terminal 3031 need only beconfigured for multiple participation in the premises, peripheral andvehicular LANs and in a radio WAN, such as RAM Mobile Data, CDPD, MTEL,ARDIS, satellite communication, etc. The storage terminal 3031, althoughalso capable of premises and peripheral LAN participation, need only beconfigured for vehicular LAN participation.

Prior to making a delivery, the truck enters a docking area for loading.As goods are loaded into the truck, the information regarding the goodsis down-loaded into the storage terminal 3031 via the terminal 3007 orcode reader 3009 (FIG. 28 a) via the premises or peripheral LANcommunications. This loading might also be accomplished automatically asthe forklift 3014 comes into range of the delivery truck 3033,establishes or joins the peripheral LAN, and transmits the previouslycollected data as described above in relation to FIG. 28 a. Alternately,loading might also be accomplished via the premises LAN.

As information regarding a good is received and stored, the storageterminal 3031 might also request further information regarding any orall of the goods via the peripheral LAN's link to the host computer 3011through the premises LAN. More likely however, the storage terminal 3031if appropriately configured would participate on the premises LAN tocommunicate directly with the host computer 3011 to retrieve suchinformation.

The peripheral LAN access point 3021 if located on the dock couldprovide a direct low power peripheral LAN connection to the backbone LAN3019 and to the host computer 3011. Specifically, in one embodiment, theaccess point 3021 is located on the dock and comprises a low power(“short hop”) radio operating in a frequency hopping mode over a 902-928MHz frequency band. However, the access point 3021 can instead beconfigured to communicate using, for example, infrared, UHF, 2.4 GHz or902 MHz spread spectrum direct sequence frequencies.

Once fully loaded and prior to leaving the dock, the storage device 3031may generate a printout of the information relating to the loaded goodsvia a peripheral LAN established with the printer 3013 on the dock. Inaddition, the information may be transmitted via the peripheral LANmodem 3023 to a given destination site.

As illustrated in FIG. 28 c, once the storage terminal 3031 andhand-held terminal 3007 moves out of range of the premises andperipheral LANs, i.e., the truck 3033 drives away from the dock, thevehicular LAN can only gain access to the premises LAN via the morecostly radio WAN communication. Thus, although the storage terminal 3031might only be configured with relaying control point functionality, tominimize radio WAN communication, the storage terminal 3031 can beconfigured to store relatively large amounts of information and toprovide processing power. Thus, the terminal 3007 can access suchinformation and processing power without having to access devices on thepremises LAN via the radio WAN.

Upon reaching the destination, the storage terminal 3031 may participatein any in range peripheral and premises LAN at the delivery site dock.Specifically, as specific goods are unloaded, they are scanned fordelivery verification, preventing delivery of unwanted goods. The driveris also informed if goods that should have been delivered are still inthe truck. As this process takes place, a report can also be generatedvia a peripheral or premises LAN printer at the destination dock forreceipt signature. Similarly, the peripheral LAN modem on thedestination dock can relay the delivery information back to the hostcomputer 3011 for billing information or gather additional informationneeded, avoiding use of the radio WAN.

If the truck 3033 is used for service purposes, the truck 3033 leavesthe dock in the morning with the addresses and directions of the servicedestinations, technical manuals, and service notes which have beenselectively downloaded from the host computer 3011 via either thepremises or peripheral LAN to the storage terminal 3031 which may beconfigured with a hard drive and substantial processing power. Uponpulling out of range, the storage terminal 3031 and the computerterminal 3007 automatically form an independent, detached vehicular LAN.Alternately, the terminals 3007 and 3031 may have previously formed thevehicular LAN before leaving dock. In one embodiment, the vehicular LANoperates using frequency hopping protocol much the same as that of thepremises LAN, with the storage terminal 3031 acting much like thepremises LAN access points. Thus, the radio transceiver circuitry forthe premises LAN participation may also be used for the vehicular LANand, as detailed above, a peripheral LAN. Similarly, if the radio WANchosen has similar characteristics, it may to be incorporated into asingle radio transceiver.

At each service address, the driver collects information using theterminal 3007 either as the data is collected, if within vehicular LANtransmission range of the storage terminal 3031, or as soon as theterminal 3007 comes within range. Any stored information within storageterminal 3031 may be requested via the vehicular LAN by the hand-heldterminal 3007. Information not stored within the vehicular LAN may becommunicated via a radio WAN as described above.

Referring again to FIG. 28 b, upon returning to the dock, the storageterminal 3031, also referred to herein as a vehicle terminal, joins inor establishes a peripheral LAN with the peripheral LAN devices on thedock, if necessary. Communication is also established via the premisesLAN. Thereafter, the storage terminal 3031 automatically transfers theservice information to the host computer 3011 which uses the informationfor billing and in formulating service destinations for automaticdownloading the next day.

FIG. 29 a is a diagrammatic illustration of another embodiment using aperipheral LAN to supporting roaming data collection by an operatoraccording to the present invention. As an operator 3061 roams thewarehouse floor he carries with him a peripheral LAN comprising theterminal 3007, code reader 3009 and a portable printer 3058. Theoperator collects information regarding goods, such as the box 3010,with the code reader 3009 and the terminal 3007. If the power resourcesare equal, the terminal 3007 may be configured and designated to alsoparticipate in the premises LAN.

Corresponding information to the code data must be retrieved from thehost computer 3011. The collected code information and retrievedcorresponding information can be displayed on the terminal 3007. Afterviewing for verification, the information can be printed on the printer3058. Because of this data flow requirement, the computer terminal 3007is selected as the peripheral LAN device which must also carry theresponsibility of communicating with the premises LAN.

If during collection, the operator decides to power down the computerterminal 3007 because it is not needed, the peripheral LAN becomesdetached from the premises LAN. Although it might be possible for thedetached peripheral LAN to function, all communication with the hostcomputer 3011 through the premises LAN is placed in a queue awaitingreattachment. As soon as the detached peripheral LAN comes within rangeof an attached peripheral LAN device, i.e., a device attached to thepremises LAN, the queued communications are relayed to the host. Itshould be clear from this description that the peripheral LAN may roamin relation to a device attached to the premises LAN (“premises LANdevice”). Similarly, the premises LAN device may roam in relation to theperipheral LAN. The roaming constitutes a relative positioning.Moreover, whenever a peripheral LAN and a master device move out ofrange of each other, the peripheral LAN may either poll for or scan foranother master device for attachment. The master device may constitute apremises LAN device, yet need not be.

To avoid detachment when the terminal 3007 is powered down, the codereader 3009 may be designated as a backup to the terminal 3007 forperforming the higher power communication with the premises LAN. Asdescribed in more detail below in reference to FIG. 33 c regarding theidle sense protocol, whenever the code reader 3009 determines that theterminal 3007 has stopped providing access to the premises LAN, the codereader 3009 will take over the role if it is next in line to perform thebackup service. Thereafter, when the computer terminal 3007 is poweredup, it monitors the peripheral LAN channel, requests and regains fromthe code reader 3009 the role of providing an interface with thepremises LAN. This, however, does not restrict the code reader 3009 fromaccessing the premises LAN although the reader 3009 may choose to usethe computer terminal 3007 for power conservation reasons.

In addition, if the computer terminal 3007 reaches a predetermined lowbattery threshold level, the terminal 3007 will attempt to pass theburden of providing premises LAN access to other peripheral LAN backupdevices. If no backup device exists in the current peripheral LAN, thecomputer terminal 3007 may refuse all high power transmissions to thepremises LAN. Alternatively, the computer terminal 3007 may eitherrefuse predetermined select types of requests, or prompt the operatorbefore performing any transmission to the premises LAN. However, thecomputer terminal 3007 may still listen to the communications from thepremises LAN and inform peripheral LAN members of waiting messages.

FIG. 29 b is a diagrammatic illustration of another embodiment of aperipheral LAN which supports roaming data collection by an operatoraccording to the present invention. An operator is equipped with aperipheral LAN 3065 comprising a housing 3067, which incorporates aprinter 3069 and a dock 3071, a roaming computing terminal 3073, and acode reader 3075. The operator may roam a warehouse floor or a shippingdock and collect and retrieve data using the peripheral LAN 3065 asdiscussed above with respect to FIG. 29 a. In this embodiment, theoperator may elect to leave the housing 3067, and hence the printer, inone area of the warehouse, or on the truck, and carry only the codereader 3075 and terminal 3073. In addition, the operator may also electto dock the terminal 3073 in the dock 3071 and carry only the codereader 3075. In any event, the terminal is capable of communicating datato the printer 3069 via RF signals or via the dock 3071.

The housing 3067 may optionally include a cigarette lighter power inputcable 3077 to power the printer 3069, and recharge the battery of theterminal 3073 via the dock 3071. The housing 3067 may also optionallyinclude a wide area network radio to permit communication with a remotewarehouse or station 3079. In addition, the housing 3067 may also beconfigured to include the functionality of the storage terminal 3031discussed above with respect to FIGS. 28 b and 28 c.

The peripheral LAN embodiments of FIGS. 29 a and 29 b may, of course,function when detached from the premises LAN. This feature isparticularly desirable in situations where attachment to the premisesLAN may be more costly, such as, for example, during the remote pick-upor delivery of goods by a driver. In the situation where a driver ispicking up goods, the driver may, for example, use the code reader andterminal to collect and/or enter information regarding the goods, suchas their origin, destination, weight, etc. The terminal may then encodethe information, and transmit it to the printer so that the driver canlabel each box appropriately with a bar or other type of code for lateridentification and routing of the goods.

Once information regarding a particular pick-up has been stored, eitherin the terminal or storage terminal, the driver may download the storeddata using the WAN radio to the premises LAN host computer at the remotewarehouse or station 3079 so that the information may be used topre-schedule further routing of the goods before the driver evenarrives. Because WAN communication is costly, however, the informationmay instead be automatically transferred wirelessly to the premises LANhost once the driver comes into range of the premises LAN, as discussedabove with respect to FIG. 28 b. Alternatively, or as a check to verifyinformation previously transmitted to the premises LAN wirelessly, theinformation may be downloaded from the terminal to the premises LAN hostvia a docking system 3081 located at the warehouse or station 3079. Thedocking system 3081 may also be used to recharge the terminals 3073.

Once the host computer has the information regarding the goods picked upby the driver(s), the host can download the data via RF or the dockingsystem 3081 to any number of terminals 3073 used by warehouse personnelwho unload the trucks. While unloading, these personnel can, forexample, use a terminal 3073 and a code reader 3075 to build containersfor further distribution of the goods to various destinations.Specifically, as a container is unloaded, the label previously placed onthe container by the driver is scanned by the code reader 3075, anddestination information is displayed on the terminal 3073. The box maythen be taken to and loaded into the container headed for the samedestination. Each container may also have a label which can be scannedto verify the destination of that particular container.

FIG. 30 is a block diagram illustrating the functionality of RFtransceivers built in accordance with the present invention. Althoughpreferably plugging into PCMCIA slots of the computer terminals andperipherals, the transceiver 3110 may also be built-in or externallyattached via available serial, parallel or ethernet connectors forexample. Although the transceivers used by potential peripheral LANmaster devices may vary from those used by peripheral LAN slave devices(as detailed below), they all contain the illustrated functional blocks.

In particular, the transceiver 3110 contains a radio unit 3112 whichattaches to an attached antenna 3113. The radio unit 3112 used inperipheral LAN slave devices need only provide reliable low powertransmissions, and are designed to conserve cost, weight and size.Potential peripheral LAN master devices not only require the ability tocommunicate with peripheral LAN slave devices, but also require higherpower radios to also communicate with the premises LAN. Thus, potentialperipheral LAN master devices and other non-peripheral LAN slave devicesmight contain two radio units 3112 or two transceivers 3110—one servingthe premises LAN and the other serving the peripheral LAN—else onlycontain a single radio unit to service both networks.

In embodiments where cost and additional weight is not an issue, a dualradio unit configuration for potential peripheral LAN master devices mayprovide several advantages. For example, simultaneous transceiveroperation is possible by choosing a different operating band for eachradio. In such embodiments, a 2.4 GHz radio is included for premises LANcommunication while a 27 MHz radio supports the peripheral LAN.Peripheral LAN slave devices receive only the 27 MHz radio, while thenon-potential peripheral LAN participants from the premises LAN arefitted with only the 2.4 GHz radios. Potential peripheral LAN masterdevices receive both radios. The low power 27 MHz peripheral LAN radiois capable of reliably transferring information at a range ofapproximately 40 to 100 feet asynchronously at 19.2 KBPS. An additionalbenefit of using the 27 MHz frequency is that it is an unlicensedfrequency band. The 2.4 GHz radio provides sufficient power (up to 1Watt) to communicate with other premises LAN devices. Another benefit ofchoosing 2.4 GHz or 27 MHz bands is that neither require FCC licensing.Many different frequency choices could also be made such as the 900 MHzband, UHF, etc. Alternatively, infrared communication may be used insituations where line of sight may be achieved between devices on thenetwork.

In embodiments where cost and additional weight are at issue, a singleradio unit configuration is used for potential peripheral LAN masterdevices. Specifically, in such embodiments, a dual mode 2.4 GHz radiosupports both the peripheral LAN and premises LANs. In a peripheral LANmode, the 2.4 GHz radio operates at a single frequency, low power level(sub-milliwatt) to support peripheral LAN communication at relativelyclose distances 20-30 feet). In a high power (up to 1 Watt) or mainmode, the 2.4 GHz radio provides for frequency-hopping communicationover relatively long distance communication connectivity with thepremises LAN. Although all network devices might be fitted with such adual mode radio, only peripheral LAN master devices use both modes.Peripheral LAN slave devices would only use the low power mode while allother premises LAN devices would use only the high power mode. Becauseof this, to save cost, peripheral LAN slave devices are fitted with asingle mode radio operating in the peripheral LAN mode. Non-peripheralLAN participants are also fitted with a single mode (main mode) radiounit for cost savings.

Connected between the radio unit 3112 and an interface 3110, amicroprocessor 3120 controls the information flow between through thetransceiver 3110. Specifically, the interface 3115 connects thetransceiver 3110 to a selected computer terminal, a peripheral device orother network device. Many different interfaces 3115 are used and thechoice will depend upon the connection port of the device to which thetransceiver 3110 will be attached. Virtually any type of interface 3110could be adapted for use with the transceiver 3110 of the presentinvention. Common industry interface standards include RS-232, RS-422,RS-485, 10BAS2 Ethernet, 10BASE5 Ethernet, 10BASE-T Ethernet, fiberoptics, IBM 4/16 Token Ring, V.11, V.24, V.35, Apple Localtalk andtelephone interfaces. In addition, via the interface 3115, themicroprocessor 3120 maintains a radio independent, interface protocolwith the attached network device, isolating the attached device from thevariations in radios being used.

The microprocessor 3120 also controls the radio unit 3112 to accommodatecommunication with the either the premises LAN, the peripheral LAN, orboth (for dual mode radios). Moreover, the same radio might also be usedfor vehicular LAN and radio WAN communication as described above. Forexample, a radio located in a vehicle or in a hand held terminal can beconfigured to communicate not only within a local network, but mightalso be capable of receiving paging messages.

More specifically, in a main mode transceiver, the microprocessor 3120utilizes a premises LAN protocol to communicate with the premises LAN.Similarly, in a peripheral LAN mode transceiver, the microprocessor 3120operates pursuant to a peripheral LAN protocol to communicate in theperipheral LAN. In the dual mode transceiver, the microprocessor 3120manages the use of and potential conflicts between both the premises andperipheral LAN protocols. Detail regarding the premises and peripheralLAN protocols can be found in reference to FIGS. 33-36 below.

In addition, as directed by the corresponding communication protocol,the microprocessor 3120 controls the power consumption of the radio3112, itself and the interface 3115 for power conservation. This isaccomplished in two ways. First, the peripheral LAN and premisesprotocols are designed to provide for a low power mode or sleep modeduring periods when no communication involving the subject transmitteris desired as described below in relation to FIGS. 33-34. Second, bothprotocols are designed to adapt in both data rate and transmission powerbased on power supply (i.e., battery) parameters and range informationas described in reference to FIGS. 35-36.

In order to insure that the proper device is receiving the informationtransmitted, each device is assigned a unique address. Specifically, thetransceiver 3110 can either have a unique address of its own or can usethe unique address of the device to which it is attached. The uniqueaddress of the transceiver can either be one selected by the operator orsystem designer or one which is permanently assigned at the factory suchas an IEEE address. The address 3121 of the particular transceiver 3110is stored with the microprocessor 3120.

In the illustrated embodiments of FIGS. 28-29 b, the peripheral LANmaster device is shown as being either a peripheral LAN access point ora mobile or portable computer terminal. From a data flow viewpoint, inconsidering the fastest access through the network, such choices for theperipheral LAN master devices appear optimal. However, any peripheralLAN device might be assigned the role of the master, even those that donot seem to provide an optimal data flow pathway but may provide foroptimal battery usage. For example, in the personal peripheral LAN ofFIG. 29 a, because of the support from the belt 3059, the printer mightcontain the greatest battery capacity of the personal peripheral LANdevices. As such, the printer might be designated the peripheral LANmaster device and be fitted with either a dual mode radio or two radiosas master devices require. The printer, or other peripheral LAN slavedevices, might also be fitted with such required radios to serve only asa peripheral LAN master backup. If the battery power on the actualperipheral LAN master, i.e., the hand-held terminal 3007 (FIG. 29 a,drops below a preset threshold, the backup master takes over.

FIG. 31 is a drawing which illustrates an embodiment of the personalperipheral LAN shown in FIG. 29 a which designates a printer as theperipheral LAN master device. Specifically, in a personal peripheral LAN3165, a computer terminal 3170 is strapped to the forearm of theoperator. A code reader 3171 straps to the back of the hand of the userand is triggered by pressing a button 3173 with the thumb. Because oftheir relatively low battery energy, the computer terminal 3170 and codereader 3171 are designated peripheral LAN slave devices and each containa peripheral LAN transceiver having a broadcast range of two meters orless. Because of its greater battery energy, the printer 3172 contains adual mode radio and is designated the peripheral LAN master device.

FIG. 32 is a block diagram illustrating a channel access algorithm usedby peripheral LAN slave devices according to the present invention. At ablock 3181, when a slave device has a message to send, it waits for anidle sense message to be received from the peripheral LAN master deviceat a block 3183. When an idle sense message is received, the slavedevice executes a back-off protocol at a block 3187 in an attempt toavoid collisions with other slave devices waiting to transmit.Basically, instead of permitting every slave device from repeatedlytransmitting immediately after an idle sense message is received, eachwaiting slave is required to first wait for a pseudo-random time periodbefore attempting a transmission. The pseudo-random back-off time periodis generated and the waiting takes place at a block 3187. At a block3189, the channel is sensed to determine whether it is clear fortransmission. If not, a branch is made back to the block 3183 to attempta transmission upon receipt of the next idle sense message. If thechannel is still clear, at a block 3191, a relatively small “request tosend” type packet is transmitted indicating the desire to send amessage. If no responsive “clear to send” type message is received fromthe master device, the slave device assumes that a collision occurred ata block 3193 and branches back to the block 3183 to try again. If the“clear to send” message is received, the slave device transmits themessage at a block 3195.

Several alternate channel access strategies have been developed forcarrier sense multiple access (CSMA) systems and include 1-persistent,non-persistent and p-persistent. Such strategies or variations thereofcould easily be adapted to work with the present invention.

FIG. 33 a is a timing diagram of the protocol used according to oneembodiment the present invention illustrating a typical communicationexchange between a peripheral LAN master device having virtuallyunlimited power resources and a peripheral LAN slave device. Time line3201 represents communication activity by the peripheral LAN masterdevice while time line 3203 represents the corresponding activity by theperipheral LAN slave device. The master periodically transmits an idlesense message 3205 indicating that it is available for communication orthat it has data for transmission to a slave device. Because the masterhas virtually unlimited power resources, it “stays awake” for the entiretime period 3207 between the idle sense messages 3205. In other words,the master does not enter a power conserving mode during the timeperiods 3207.

The slave device uses a binding protocol (discussed below with regard toFIG. 33c) to synchronize to the master device so that the slave mayenter a power conserving mode and still monitor the idle sense messagesof the master to determine if the master requires servicing. Forexample, referring to FIG. 33 a, the slave device monitors an idle sensemessage of the master during a time period 3209, determines that noservicing is required, and enters a power conserving mode during thetime period 3211. The slave then activates during a time period 3213 tomonitor the next idle sense message of the master. Again, the slavedetermines that no servicing is required and enters a power conservingmode during a time period 3215. When the slave activates again during atime period 3217 to monitor the next idle sense message, it determinesfrom a “request to send” type message from the master that the masterhas data for transmission to the slave. The slave responds by sending a“clear to send” type message during the time period 3217 and staysactivated in order to receive transmission of the data. The master isthus able to transmit the data to the slave during a time period 3219.Once the data is received by the slave at the end of the time period3221, the slave again enters a power conserving mode during a timeperiod 3223 and activates again during the time period 3225 to monitorthe next idle sense message.

Alternatively, the slave may have data for transfer to the master. Ifso, the slave indicates as such to the master by transmitting a messageduring the time period 3217 and then executes a backoff algorithm todetermine how long it must wait before transmitting the data. The slavedetermines from the backoff algorithm that it must wait the time period3227 before transmitting the data during the time period 3221. The slavedevices use the backoff algorithm in an attempt to avoid the collisionof data with that from other slave devices which are also trying tocommunicate with the master. The backoff algorithm is discussed morefully above in reference to FIG. 32.

The idle sense messages of the master may also aid in schedulingcommunication between two slave devices. For example, if a first slavedevice has data for transfer to a second slave device, the first slavesends a message to the master during the time period 3209 requestingcommunication with the second slave. The master then broadcasts therequest during the next idle sense message. Because the second slave ismonitoring the idle sense message, the second slave receives the requestand stays activated at the end of the idle sense message in order toreceive the communication. Likewise, because the first slave is alsomonitoring the idle sense message, it too receives the request and staysactivated during the time period 3215 to send the communication.

FIG. 33 b is a timing diagram of the protocol used according to oneembodiment of the present invention illustrating a typical communicationexchange between a peripheral LAN master having limited power resourcesand a peripheral LAN slave device. This exchange is similar to thatillustrated in FIG. 33 a except that, because it has limited powerresources, the master enters a power conserving mode. Beforetransmitting an idle sense message, the master listens to determine ifthe channel is idle. If the channel is idle, the master transmits anidle sense message 3205 and then waits a time period 3231 to determineif any devices desire communication. If no communication is desired, themaster enters a power conserving mode during a time period 3233 beforeactivating again to listen to the channel. If the channel is not idle,the master does not send the idle sense message and enters a powersaving mode for a time period 3235 before activating again to listen tothe channel.

Communication between the master and slave devices is the same as thatdiscussed above in reference to FIG. 33 a except that, after sending orreceiving data during the time period 3219, the master device enters apower conserving mode during the time period 3237.

FIG. 33 c is also a timing diagram of one embodiment of the protocolused according to the present invention which illustrates a scenariowherein the peripheral LAN master device fails to service peripheral LANslave devices. The master device periodically sends an idle sensemessage 3205, waits a time period 3231, and enters a power conservingmode during a time period 3233 as discussed above in reference to FIG.33 b. Similarly, the slave device monitors the idle sense messagesduring time periods 3209 and 3213 and enters a power conserving modeduring time periods 3211 and 3215. For some reason, however, the masterstops transmitting idle sense messages. Such a situation may occur, forexample, if the master device is portable and is carried outside therange of the slave's radio. During a time period 3241, the slaveunsuccessfully attempts to monitor an idle sense message. The slave thengoes to sleep for a time period 3243 and activates to attempt to monitora next idle sense message during a time period 3245, but is againunsuccessful.

The slave device thereafter initiates a binding protocol to attempt toregain synchronization with the master. While two time periods 3241 and3245 are shown, the slave may initiate such a protocol after any numberof unsuccessful attempts to locate an idle sense message. With thisprotocol, the slave stays active for a time period 3247, which is equalto the time period from one idle sense message to the next, in anattempt to locate a next idle sense message. If the slave is againunsuccessful, it may stay active until it locates an idle sense messagefrom the master, or, if power consumption is a concern, the slave mayenter a power conserving mode at the end of the time period 3247 andactivate at a later time to monitor for an idle sense message.

In the event the master device remains outside the range of the slavedevices in the peripheral LAN for a period long enough such thatcommunication is hindered, one of the slave devices may take over thefunctionality of the master device. Such a situation is useful when theslave devices need to communicate with each other in the absence of themaster. Preferably, such a backup device has the ability to communicatewith devices on the premises LAN. If the original master returns, itlistens to the channel to determine idle sense messages from the backup,indicates to the backup that it has returned and then begins idle sensetransmissions when it reestablishes dominance over the peripheral LAN.

FIG. 34 is a timing diagram illustrating one embodiment of theperipheral LAN master device's servicing of both the high poweredpremises LAN and the low powered peripheral LAN subnetwork, with asingle or plural radio transceivers, in accordance with presentinvention. Block 3251 represents typical communication activity of themaster device. Line 3253 illustrates the master's communication with anaccess point on the premises LAN while line 3255 illustrates themaster's communication with a slave device on the peripheral LAN. Lines3257 and 3259 illustrate corresponding communication by the access pointand slave device, respectively.

The access point periodically broadcasts HELLO messages 3261 indicatingthat it is available for communication. The master device monitors theHELLO messages during a time period 3263, and, upon determining that thebase does not need servicing, enters a power conserving mode during atime period 3265. The master then activates for a time period to monitorthe next HELLO message from the base. If the master has data to send tothe base, it transmits the data during a time period 3271. Likewise, ifthe base has data to send to the master, the base transmits the dataduring a time period 3269. Once the data is received or sent by themaster, it may again enter a power conserving mode. While HELLO messageprotocol is discussed, a number of communication protocols may be usedfor communication between the base and the master device. As may beappreciated, the peripheral LAN master device acts as a slave to accesspoints in the premises LAN.

Generally, the communication exchange between the master and the slaveis similar to that described above in reference to FIG. 33 b. Block3273, however, illustrates a situation where the master encounters acommunication conflict, i.e., it has data to send to or receive from theslave on the peripheral LAN at the same time it will monitor thepremises LAN for HELLO messages from the base. If the master has tworadio transceivers, the master can service both networks. If, however,the master only has one radio transceiver, the master chooses to serviceone network based on network priority considerations. For example, inblock 3273, it may be desirable to service the slave because of thepresence of data rather than monitor the premises LAN for HELLO messagesfrom the base. On the other hand, in block 3275, it may be moredesirable to monitor the premises LAN for HELLO messages rather thantransmit an idle sense message on the peripheral LAN.

FIGS. 35 and 36 are block diagrams illustrating additional power savingfeatures according to the present invention, wherein ranging and batteryparameters are used to optimally select the appropriate data rate andpower level for subsequent transmissions. Specifically, even thoughnetwork devices such as the computer terminal 3007 in FIGS. 28-29 b havethe capability of performing high power transmissions, because ofbattery power concerns, such devices are configured to utilize minimumtransmission energy. Adjustments are made based on ranging informationand on battery parameters. Similarly, within the peripheral LAN, eventhough lower power transceivers are used, battery conservation issuesalso justify the use of such data rate and power adjustments. Thisprocess is described in more detail below in reference to FIGS. 35 and36.

More specifically, FIG. 35 is a block diagram which illustrates aprotocol 3301 used by a destination peripheral LAN device and acorresponding protocol 3303 used by a source peripheral LAN device toadjust the data rate and possibly the power level for futuretransmission between the two devices. At a block 3311, upon receiving atransmission from a source device, the destination device identifies arange value at a block 3313. In a low cost embodiment, the range valueis identified by considering the received signal strength indications(RSSI) of the incoming transmission. Although RSSI circuitry might beplaced in all peripheral LAN radios, the added expense may require thatonly peripheral LAN master devices receive the circuitry. This wouldmean that only peripheral LAN master devices would perform the functionof the destination device. Other ranging techniques or signal qualityassessments can also be used, such as measuring jitter in receivedsignals, by adding additional functionality to the radios. Finally,after identifying the range value at the block 3313, the destinationdevice subsequently transmits the range value to the slave device fromwhich the transmission was received, at a block 3314.

Upon receipt of the range value from the destination device at a block3321, the source peripheral LAN device evaluates its battery parametersto identify a subsequent data rate for transmission at a block 3323. Ifrange value indicates that the destination peripheral LAN device is verynear, the source peripheral LAN device selects a faster data rate. Whenthe range value indicates a distant master, the source device selects aslower rate. In this way, even without adjusting the power level, thetotal energy dissipated can be controlled to utilize only that necessaryto carry out the transmission. However, if constraints are placed on themaximum or minimum data rates, the transmission power may also need tobe modified. For example, to further minimize the complexity associatedwith a fully random range of data rate values, a standard range and setof several data rates may be used. Under such a scenario, a transmissionpower adjustment might also need to supplement the data rate adjustment.Similarly, any adjustment of power must take into consideration maximumand minimum operable levels. Data rate adjustment may supplement suchlimitations. Any attempted modification of the power and data rate mighttake into consideration any available battery parameters such as thosethat might indicate a normal or current battery capacity, the drain onthe battery under normal conditions and during transmission, or the factthat the battery is currently being charged. The latter parameter provesto be very significant in that when the battery is being charged, theperipheral LAN slave device has access to a much greater power sourcefor transmission, which may justify the highest power transmission andpossibly the slowest data rate under certain circumstances.

Finally, at a block 3325, an indication of the identified data rate istransmitted back to the destination device so that future transmissionsmay take place at the newly selected rate. The indication of data ratemay be explicit in that a message is transmitted designating thespecific rate. Alternately, the data rate may be transferred implicitlyin that the new rate is chose and used by the source, requiring thedestination to adapt to the change. This might also be done using apredefined header for synchronization.

In addition, at the block 3325, in another embodiment, along with theindication of the identified data rate, priority indications are also becommunicated. Whenever battery power is detected as being low, a radiotransmits a higher priority indication, and each receiver thereaftertreats the radio as having a higher protocol priority than other suchradios that exhibit normal power supply energy. Thus, the remainingbattery life is optimized. For example, in a non-polling network, thelow power device might be directly polled periodically so to allowscheduled wake-ups and contention free access to a receiver. Similarly,in an alternate embodiment, priority indications not need to be sent.Instead, the low battery power device itself exercises protocolpriority. For example, for channel access after detecting that thechannel is clear at the end of an ongoing transmission, devices withnormal energy levels are required to undergo a pseudo-randot back-offbefore attempting a transmission (to avoid collision). The low powerdevice may either minimize the back-off period or ignore the back-offperiod completely. Thus, the low power device gains channel accesseasier than other normal power level devices. Other protocol priorityschemes may also be assigned by the receivers to the low power device(via the indication), else may be taken directly by the low powerdevice.

FIG. 36 illustrates an alternate embodiment for carrying out the datarate and possibly power level adjustment. At a block 3351 upon bindingand possibly periodically, the source peripheral LAN device sends anindication of its current battery parameters to the destinationperipheral LAN device. This indication may be each of the parameters ormay be an averaged indication of all of the parameters together. At ablock 3355, upon receipt, the destination peripheral LAN device 355stores the battery parameters (or indication). Finally, at a block 3358,upon receiving a transmission from the source device, based on rangedeterminations and the stored battery parameters, the destinationterminal identifies the subsequent data rate (and possibly power level).Thereafter, the new data rate and power level are communicated to thesource device either explicitly or implicitly for future transmissions.

FIG. 37 illustrates an exemplary block diagram of a radio unit 3501capable of concurrent participation on multiple LAN's. To transmit, acontrol processor 3503 sends a digital data stream to a modulationencoding circuit 3505. The modulation encoding circuit 3505 encodes thedata stream in preparation for modulation by frequency translationcircuit 3507. The carrier frequency used to translate the data stream isprovided by a frequency generator circuit 3509. Thereafter, themodulated data stream is amplified by a transmitter amplifier circuit3511 and then radiated via the one of a plurality of antennas 3513 thathas been selected via an antenna switching circuit 3515. Together, themodulation encoding circuitry 3505, translator 3507, amplifier 3511 andassociated support circuitry constitute the transmitter circuitry.

Similarly, to receive data, the RF signal received by the selected oneof the plurality of antennas 3513 is communicated to a receiver RFprocessing circuit 3517. After performing a rather coarse frequencyselection, the receiver RF processing circuit 3517 amplifies the RFsignal received. The amplified received signal undergoes a frequencyshift to an IF range via a frequency translation circuit 3519. Thefrequency translation circuit 3519 provides the center frequency for thefrequency shift. Thereafter, a receiver signal processing circuitreceives the IF signal, performs a more exact channel filtering anddemodulation, and forwards the received data to the control processor3503, ending the process. Together, the receiver signal processing 3521,translator 3517, receiver RF processing 3517 and associated supportcircuitry constitute the receiver circuitry.

The control processor 3503 operates pursuant to a set of softwareroutines stored in memory 3522 which may also store incoming andoutgoing data. Specifically, the memory 3522 contains routines whichdefine a series of protocols for concurrent communication on a pluralityof LANS. As part of such operation, the control processor 3503 providesfor power savings via a power source control circuit 3523, i.e.,whenever the participating protocols permit, the control processor 3503causes selective power down of the radio transceiver circuitry via acontrol bus 3525. Also via the bus 3525, the control processor sets thefrequency of the frequency generator 3509 so as to select theappropriate band and channel of operation required by a correspondinglyselected protocol. Similarly, the control processor 3503 selects theappropriate antenna (via the antenna switching circuitry 3515) andchannel filtering in preparation for operation on a selected LAN.Responding to the software routines stored in the memory 3522, thecontrol processor 3503 selects the appropriate LANs to establishparticipation, detaches from those of the selected LANs in whichparticipation is no longer needed, identifies from the selected LANs acurrent priority LAN in which to actively participate, maintains atime-shared servicing of the participating LANs. Further detailregarding this process follows below.

In one embodiment, the control processor 3503 constitutes a typicalmicroprocessor on an independent integrated circuit. In anotherembodiment, the control processor 3503 comprises a combination ofdistributed processing circuitry which could be included in a singleintegrated circuit as is a typical microprocessor. Similarly, the memory3522 could be any type of memory unit(s) or device(s) capable ofsoftware storage.

The radio circuitry illustrated is designed with the frequency nimblefrequency generator 3509 so as to be capable of operation on a pluralityof LANs/WANs. Because each of the plurality may be allocated differentfrequency bands, more than one antenna may be desirable (although asingle antenna could be used, antenna bandwidth limitations might resultin an unacceptable transmission-reception inefficiency). Thus, to selectthe appropriate configuration, the control processor 3503 firstidentifies the LAN/WAN on which to participate and selects thecorresponding radio configuration parameters from the memory 3521.Thereafter, using the configuration parameters and pursuant to controlroutines stored in the memory 3522, the control processor 3503 sets thefrequency of the generator 3509, selects the appropriate antenna via theantenna switching circuit 3515, and configures the receiver RF andsignal processing circuits 3517 and 3521 for the desired LAN/WAN.

More particularly, the antenna switching circuit 3515 comprises aplurality of digitally controlled switches, each of which is associatedwith one of the plurality of antennas 3513 so as to permit selectiveconnection by the control processor 3503 of any available antenna to thetransceiver circuitry.

FIG. 38 illustrates an exemplary functional layout of the frequencygenerator 3509 of FIG. 37 according to one embodiment of the presentinvention. Basically, the frequency generator 3509 responds to thecontrol processor 3503 by producing the translation frequency necessaryfor a selected LAN/WAN. The illustrated frequency generator comprises avoltage controlled oscillator (VCO) 3601. As is commonly known, for aVCO, the center frequency F_(VCO) tracks the input voltage. However,because typical VCO's are subject to drift, the VCO is stabilized byconnecting it in a phase locked loop to a narrowband reference, such asa crystal reference oscillator 3603. The oscillator 3603 outputs asignal of a fixed or reference frequency F_(REF) to a divide-by-Rcircuit 3605, which divides as its name implies the reference frequencyF_(REF) by the known number R. A phase detector 3609 receives thedivided-by-R output of the circuit 3609 and the feedback from the outputof the VCO 3601 via a divide-by-N circuit 3607. Upon receipt, the phasedetector 3609 compares the phase of the outputs from the circuits 3605and 3607. Based on the comparison, a phase error signal is generated andapplied to a low-pass loop filter 3611. The output of the filter 3611 isapplied to the input of the VCO 3601 causing the center frequency of theVCO 3601 to lock-in. Therefore, if the output of the VCO 3601 begins todrift out of phase of the reference frequency, the phase detector 3609responds with a corrective output so as to adjust the center frequencyof the VCO 3601 back in phase.

With the illustrated configuration, the center frequency of the VCO 3601is a function of the reference frequency as follows:F _(VCO)=(F _(REF) *N)/RThus, to vary the center frequency of the VCO 3601 to correspond to aband of a selected LAN/WAN in which active participation is desired, thecontrol processor 3503 (FIG. 37) need only vary the variables “R” and“N” and perhaps the frequency of the reference oscillator. Because theoutput F_(REF) of the reference oscillator 3603 is quite stable, thephase lock loop as shown also keeps the output frequency F_(VCO) of theVCO 3601 stable.

More specifically, although any other scheme might be implemented, thevalue R in the divide-by-R circuit 3605 is chosen so as to generate anoutput equal to the channel spacing of a desired LAN/WAN, while thevalue N is selected as a multiplying factor for stepping up the centerfrequency of the VCO 3601 to the actual frequency of a given channel.Moreover, the frequency of the reference oscillator is chosen so as tobe divisible by values of R to yield the channel spacing frequencies ofall potential LANs and WANs. For example, to participate on both MTELCorporation's Two Way Paging WAN (operating at 900 MHz with 25 KHz and50 KHz channel spacings) and ARDIS Corporation's 800 MHz specializedmobile radio (SMR) WAN (operating at 25 KHz channel spacings centered atmultiples of 12.5 KHz), a single reference frequency may chosen to be awhole multiple of 12.5 KHz. Alternately, multiple reference frequenciesmay be chosen. Moreover, the value N is chosen to effectively multiplythe output of the divide-by-R circuit 3605 to the base frequency of agiven channel in the selected WAN.

For frequency hopping protocols, the value of R is chosen so as to yieldthe spacing between frequency hops. Thus, as N is incremented, eachhopping frequency can be selected. Randomizing the sequence of suchvalues of N provides a hopping sequence for use by an access point asdescribed above. Pluralities of hopping sequences (values of N) may bestored in the memory 3522 (FIG. 37) for operation on the premises LAN,for example.

In addition to the single port phase locked loop configuration for thefrequency generator 3509, other configurations might also beimplemented. Exemplary circuitry for such configurations can be found inU.S. patent application Ser. No. 08/205,639, filed Mar. 4, 1994 byMahany et al., entitled “Method of and Apparatus For ControllingModulation of Digital Signals in Frequency-Modulated Transmissions”.This application is incorporated herein in its entirety.

FIG. 39 illustrates further detail of the receiver RF processing circuit3517 of FIG. 37 according to one embodiment of the present invention.Specifically, a preselector 3651 receives an incoming RF data signalfrom a selected one of the plurality of antennas 3513 (FIG. 37) via aninput line 3653. The preselector 3651 provides a bank of passive filters3657, such as ceramic or dielectric resonator filters, each of whichprovides a coarse filtering for one of the LAN/WAN frequencies to whichit is tuned. One of the outputs from the bank of passive filters 3657 isselected by the control processor 3503 via a switching circuit 3655 soas to monitor the desired one of the available LANs/WANs. Thereafter,the selected LAN/WAN RF signal is amplified by an RF amplifier 3659before translation by the frequency translation circuit 3519 (FIG. 37).

FIG. 40 illustrates further detail of the receiver signal processingcircuit 3521 of FIG. 37 according to one embodiment of the presentinvention. In particular, digitally controlled switching circuits 3701and 3703 respond to the control processor 3503 by selecting anappropriate pathway for the translated IF data signal through one of abank of IF filters 3705. Each IF filter is an analog crystal filter,although other types of filters such as a saw filter might be used. TheIF filters 3705 provide rather precise tuning to select the specificchannel of a given LAN/WAN.

After passing through the switching circuit 3703, the filtered IF datasignal is then amplified by an IF amplifier 3707. The amplified IFsignal is then communicated to a demodulator 3709 for demodulation. Thecontrol processor retrieves the incoming demodulated data signal forprocessing and potential storage in the memory 3522 (FIG. 37).

FIG. 41 illustrates further detail of the receiver signal processingcircuit 3521 of FIG. 37 according to another embodiment of the presentinvention. Specifically, the IF signal resulting from the translation bythe frequency translator circuitry 3519, enters the receiver signalprocessing circuit via an input 3751. Thereafter, the IF signal passesthrough an anti-aliasing filter 3753, and is amplified by a linearamplifier 3755. An IF oscillator 3757 supplies a reference signalf_(REF) for translation of the incoming IF signal at frequencytranslation circuits 3759 and 3761. A phase shift circuit 3763 providesfor a 90 degree shift of f_(REF), i.e., if f_(REF) is considered a SINEwave, then the output of the circuit 3763 is the COSINE of f_(REF), Boththe SINE and COSINE frequency translation pathways provide for channelselection of the incoming data signal. Thereafter the data signals arepassed through corresponding low pass filters 3765 and 3767 inpreparation for sampling by analog to digital (A/D) converters 3769 and3771. Each A/D converter forwards the sampled data to a digital signalprocessor 3773 which provides for further filtering and demodulation.The digital signal processor 3773 thereafter forwards the incoming datasignal to the control processor 3503 (FIG. 37) via an output line 3775.Moreover, although the digital signal processor 3773 and the controlprocessor 3507 are discrete components in the illustrated example, theymay also be combined into a single integrated circuit.

FIG. 42 illustrates further detail of some of the storage requirementsof the memory 3522 of FIG. 37 according to one embodiment of the presentinvention. To control the radio, the control processor 3503 (FIG. 37)accesses the information in the memory 3522 needed for radio setup andoperation on a plurality of LANs/WANs. Among other information, thememory 3522 stores: 1) a plurality of software protocols, one for eachLAN/WAN to be supported, which define how the radio is to participate onthe corresponding LAN; and 2) an overriding control set of routineswhich govern the selection, use and interaction of the plurality ofprotocols for participation on desired LANs/WANs.

Specifically, in the memory unit 3522, among other information androutines, software routines relating to the media access control (MAC)sublayer of the communication protocol layers can be found. In general,a MAC sublayer provides detail regarding how communication generallyflows through a corresponding LAN or WAN. Specifically, the MAC sublayerhandles functions such as media access control, acknowledge, errordetection and retransmission. The MAC layer is fairly independent of thespecific radio circuitry and channel characteristics of the LAN or WAN.

As illustrated, premises LAN, peripheral LAN, vehicular LAN and WAN MACroutines 3811, 3813, 3815 and 3817 provide definition as to how thecontrol processor 3503 (FIG. 37) should operate while activelyparticipating on each LAN or WAN. Although only the several sets of MACroutines are shown, many other sets might also be stored or down-loadedinto the memory 3522. Moreover, the sets of MAC routines 3811-17 mightalso share a set of common routines 3819. In fact, the sets of MACroutines 3811-17 might be considered a subset of an overall MAC whichshares the common MAC routines 3819.

Below the MAC layer in the communication hierarchy, hardware and channelrelated software routines and parameters are necessary for radiocontrol. For example, such routines govern the specific switching forchannel filtering and antenna selection required by a given LAN or WAN.Similarly, these routines govern the control processor 3503's selectionof parameters such as for R and N for the frequency generator 3509 (FIG.38), or the selective power-down (via the power source control circuitry3503—FIG. 37) of portions or all of the radio circuitry wheneverpossible to conserve battery power. As illustrated, such routines andparameters are referred to as physical (PHY) layer control software3821. Each of the sets of MAC routines 3811-17 and 3819 provide specificinteraction with the PHY layer control software 3821.

A set of MAC select/service routines 3823 govern the management of theoverall operation of the radio in the network. For example, ifparticipation on the premises LAN is desired, the MAC select/serviceroutines 3823 direct the control processor 3503 (FIG. 37) to the commonand premises MAC routines 3819 and 3811 respectively. Thereafter, ifconcurrent participation with a peripheral LAN is desired, theselect/service routines 3823 direct the control processor 3503 to entera sleep mode (if available). The control processor 3503 refers to thepremises LAN MAC routines 3811, and follows the protocol necessary toestablish sleep mode on the premises LAN. Thereafter, the select/serviceroutines 3823 directs the control processor 3503 to the peripheral LANMAC routines 3813 to establish and begin servicing the peripheral LAN.Whenever the peripheral LAN is no longer needed, the select/serviceroutines 3823 direct a detachment from the peripheral LAN (if required)as specified in the peripheral LAN MAC routines 3813. Similarly, ifduring the servicing of the peripheral LAN a overriding need to servicethe premises LAN arises, the processor 3503 is directed to enter a sleepmode via the peripheral LAN MAC routines 3813, and to return toservicing the premises LAN.

Although not shown, additional protocol layers as well as incoming andoutgoing data are also stored with the memory 3522, which, as previouslyarticulated, may be a distributed plurality of storage devices.

FIG. 43 illustrates a software flow chart describing the operation ofthe control processor 3503 (FIG. 37) in controlling the radio unit toparticipate on multiple LANs according to one embodiment of the presentinvention. Specifically, at a block 3901, the control processor firstdetermines whether the radio unit needs to participate on an additionalLAN (or WAN). If such additional participation is needed, at a block3903, the radio unit may register sleep mode operation with otherparticipating LANs if the protocols of those LANs so require and theradio unit has not already done so. Next, at a block 3905, the controlprocessor causes the radio unit to poll or scan to locate the desiredadditional LAN. If the additional LAN is located at a block 3907,participation of the radio unit on the additional LAN is established ata block 3909.

If additional participation is not needed at block 3901, or if theadditional LAN has not been located at block 3907, or once participationof the radio unit on the additional LAN has been established at block3909, the control processor next determines at a block 3911 whether anyof the participating LANs require servicing. If any given participatingLAN requires servicing, at a block 3913, the radio unit may be requiredby the protocol of the given LAN to reestablish an active participationstatus on that LAN, i.e., indicate to the given LAN that the radio unithas ended the sleep mode. Next, at a block 3915, the radio unit servicesthe given LAN as needed or until the servicing of another LAN takespriority over that of the given LAN. At a block 3917, the radio unit maythen be required to register sleep mode operation with the given LAN ifthe LAN's protocol so requires.

At that point, or if no participating LAN needs servicing at block 3911,the control processor determines at a block 3919 whether the radio needsto detach from any given participating LAN. If so, the radio unit mayimplicitly detach at a block 3923 if the protocol of the LAN from whichthe radio wishes to detach requires no action by the radio unit.However, at a block 3921, the radio unit may be required to establishactive participation on the LAN in order to explicitly detach at block3923. For example, such a situation may arise when a portable terminaldesires to operate on a shorter range vehicular LAN and detaches from apremises LAN. The portable terminal may be required by the protocol ofthe premises LAN to establish active communication on the premises LANto permit the radio unit to inform the premises LAN that it is detachingand can only be accessed through the vehicular LAN.

Once the radio unit is detached at block 3923, or if the radio unit doesnot need to detach from any participating LANs at block 3919, thecontrol processor returns to block 3901 to again determine whether theradio unit needs to participate on an additional LAN, and repeats theprocess.

FIG. 44 is an alternate embodiment of the software flow chart whereinthe control processor participates on a master LAN and, when needed, ona slave LAN. Specifically, at a block 3951, the control processor causesthe radio unit to poll or scan in order to locate the master LAN. If themaster LAN has not been located at a block 3953, polling or scanning forthe master LAN continues. Once the master LAN is located, participationwith the master is established at a block 3955. At a block 3957, theradio unit participates with the master LAN until the need for the radiounit to participate on the slave LAN takes precedence. When thatcondition occurs, the control processor determines at a block 3959whether participation of the radio unit on the slave network isestablished. If not, such participation is established at a block 3961.Next, at a block 3963, the radio unit services the slave LAN as neededor until the servicing of the master LAN takes priority. If the controlprocessor determines at a block 3965 that servicing of the slave LAN hasbeen completed, the radio unit detaches from the slave LAN at a block3967 and returns to block 3957 to continue participation on the masterLAN.

However, if the control processor determines at block 3965 thatservicing has not been, or may not be, completed, the radio unit doesnot detach from the slave LAN. In that case, before returning to block3957 to service the master LAN, the radio unit may be required by theprotocol of the slave LAN to register sleep mode operation with theslave LAN at a block 3969.

In another embodiment, shown in FIG. 45, the overall communicationsystem of the present invention has been adapted to service theenvironment found, for example, in a retail store. As illustrated, thepremises of the retail store are configured with a communication networkto provide for inventory control. Specifically, the communicationnetwork includes a backbone LAN 4501, a inventory computer 4511, and aplurality of cash registers located throughout the store, such as cashregisters 4503 and 4505. As illustrated, the backbone LAN 4501 is asingle wired link, such as Ethernet. However, it may be comprised ofmultiple sections of wired links with or without wireless linkinterconnects. For example, in another embodiment, each cash register4503 and 4505 is communicatively interconnected with the inventorycomputer via an infrared link.

The inventory computer 4511, which can range from a personal to mainframe computer, provides central control over the retail inventory bymonitoring the inventory status. Thus, the inventory computer 4511 mustmonitor both sales and delivery information regarding inventoried goods.To monitor sales information, the cash registers 4503 and 4505 includecode scanners, such as tethered code scanners 4507 and 4509, which readcodes on product labels or tags as goods are purchased. After receivingthe code information read from the scanners 4507 and 4509, the cashregisters 4503 and 4505 communicate sales information to the inventorycomputer 4511 via the backbone LAN 4501. To monitor deliveryinformation, when the truck 4513 makes a delivery, the informationregarding the goods delivered is communicated to the inventory computer4511 via the access point 4517. As illustrated, the access point 4517acts as a direct access point to the backbone LAN 4501, even though aseries of wireless hops might actually be required.

Upon receiving the sales information from the cash registers 4503 and4505, the inventory computer 4511 automatically debits the inventorycount of the goods sold. Similarly, upon receiving the deliveryinformation, the inventory computer 4511 automatically credits theinventory count of the goods delivered. With both the sales and deliveryinformation, the inventory computer 4511 accurately monitors theinventory of all goods stocked by the retail store. From the inventoryinformation, the inventory computer 4511 generates purchase orders forsubsequent delivery, automating the entire process.

In particular, the inventory computer 4511 receives sales informationfrom the cash registers 4503 and 4505 as detailed above. Whenever therestocking process is initiated, the inventory computer 4511 checks theretail inventory for each item sold to determine if restocking isneeded. If restocking proves necessary, the inventory computer 4511evaluating recent sales history, determines the quantity of the goodsneeded. From this information, an “inventory request” is automaticallygenerated by the inventory computer 4511. Once verified (as modified ifneeded), the inventory request is automatically forwarded by theinventory computer 4511 to the warehouse 4519. This forwarding occursvia either a telephone link using a modem 4521, or a WAN link using thebackbone LAN 4501, access point 4517, and an antenna tower 4523.

At the remote warehouse 4519, the delivery truck 4513 is loaded pursuantto the inventory request received from the inventory computer 4511.After loading, the truck 4513 travels to the premises of the retailstore. When within range of the access point 4517, the radio terminal4515 in the truck 4513 automatically gains access to the retail premisesLAN via the access point 4517 (as detailed above), and communicates ananticipated delivery list (a “preliminary invoice”), responsive to theinventory request, to the inventory computer 4511. In response, dockworkers can be notified to prepare for the arrival of the delivery truck4513. In addition, any rerouting information can be communicated to theterminal 4515 in the delivery truck 4513. If a complete rerouting isindicated, the truck 4513 may be redirected without ever having reachedthe dock.

While unloading the delivery truck 4513, codes are read from all goodsas they are unloaded using portable code readers, which may be builtinto or otherwise communicatively attached to the radio terminal 4515.The codes read are compared with and debited against the preliminaryinvoice as the goods are unloaded. This comparing and debiting occurseither solely within the terminal 4515 or jointly within the terminal4515 and the inventory computer 4511. If the codes read do notcorrespond to goods on the inventory request, or if the codes read docorrespond but are in excess of what was required by the inventoryrequest, the goods are rejected. Rejection, therefore, occurs prior tothe actual unloading of the goods from the delivery truck 4513.

At the dock, the goods received from the delivery truck 4513 undergo aconfirmation process by a dock worker who, using a radio terminal 4525configured with a code reader, reads the codes from the goods on thedock to guarantee that the proper goods, i.e., those requested pursuantto the inventory request, were actually unloaded. This extra step ofconfirmation can be eliminated, however, where the dock worker directlyparticipates in the code reading during the unloading process in thedelivery truck 4513. Similarly, the code reading within the deliverytruck 4513 could be eliminated in favor of the above described on-dockconfirmation process, but, reloading of any wrongly unloaded goods wouldbe required.

Upon confirmation of the delivery by the dock worker, a verified invoiceis automatically generated by the radio terminal 4515 and routed to theinventory computer 4511 for inventory and billing purposes. In addition,the verified invoice is routed to the warehouse 4519. Such routing mayoccur as soon as the delivery truck returns to the warehouse 4519.However, to accommodate rerouting in situations where goods have beenturned away at the retail store, the radio terminal 4515 communicatesthe final invoice immediately to the warehouse 4519. The warehouse 4519,upon receiving the final invoice, checks the final invoice with the listof goods loaded in the delivery truck 4513, and determines whetherdelivery of the remaining goods is possible. If so, the warehouse 4519reroutes the truck 4513 to the next delivery site.

The communication of the final invoice and the rerouting informationbetween the warehouse 4519 and the terminal 4515 may utilize a low costcommunication pathway through the telephone link in the premises networkof the retail store. In particular, the pathway for such communicationutilizes the access point 4517, backbone LAN 4501, inventory computer4511 and modem 4521. Alternately, the communication pathway might alsoutilize the WAN directly from the radio terminal 4515 to the warehouse4519 via the antenna tower 4523. Moreover, the antenna tower 4523 ismerely representative of a backbone network for the WAN. Depending onthe specific WAN used, the tower 4523 may actually be comprised of aplurality of towers using microwave links to span the distance betweenthe retail premises and the warehouse 4519. Similarly, satelliterelaying of the communications might also be used.

FIGS. 46 a-b illustrate a further embodiment of the communication systemof the present invention which illustrate the use of access servers thatsupport local processing and provide both data and program migration.Specifically, as with the previous figures, FIG. 46 a illustrates awireless and hardwired communication network which uses a spanning treeprotocol to provide ubiquitous coverage throughout a premises.

For example, if any network device, e.g., an end-point device such as awireless, hand-held computer terminal 4601, desires to communicate withanother network device, e.g., a hard-wired computer 4603, a routingrequest is constructed which specifically identifies the destinationdevice. After construction, the routing request is transmitted through aspanning tree pathway to the destination device.

In particular, the terminal 4601 formulates a routing requestidentifying the computer 4603. The routing request may also contain, forexample, a message or data to be delivered or a request for data orprogram code. The terminal 4601 transmits the routing request downstream(toward the root of the spanning tree) to an access device 4605. Theaccess device 4605 examines its spanning tree routing table entries,attempting to locate an upstream path to the destination deviceidentified by the request. Because no entry exists, the access device4605 transmits the routing request downstream to an access device 4607.After finding no routing table entry, the access device 46.07 routes therequest to a root access device 4609. Finding no routing table entry forthe computer 4603, the access device 4609 transmits the routing requestonto a wired LAN 4610. Using its routing table which has an entry forthe computer 4603, a root access device 4611 fields the routing requestand transmits the request upstream to an access device 4613. Likewise,the access device 4613, having an entry, sends the routing request to anaccess device 4617. Upon receipt, the access device 4617 forwards therouting request to the computer 4603.

When a network device, an end-point device for example, has a need forremotely stored program code (i.e., program objects) or data (i.e., dataobjects) such as a schematic diagram, delivery address or repair manual,the end-point device formulates a code or data request and sends it in adownstream spanning tree pathway. Unlike a routing request, data andcode requests do not have a specific destination designated. Instead,data/code requests (data requests and/or code request) only identify thespecific data or code needed. This is because the requesting device neednot know the destination of the data or code needed, promoting dynamic,spanning tree migration—as will become apparent below.

In addition, where possible, program code will be reduced to aninterpretive form. Common libraries of program objects (in an objectcode form, i.e., executable form) are stored at each network terminal,computer or access server. Upon any request for an application program,for example, first, the sequence of calls to each program object isdelivered along with a list of all program objects that are needed tofully execute the application program. Thereafter, if the specificunderlying code for any of the delivered objects is not found locally, arenewed request for the executable code for those program objects ismade. Upon delivery, the application program may be executed. Moreover,the movement of the program application and other specific programobjects are tracked and migrated as described above in relation togeneric data.

For example, the terminal 4667 typically operates using an applicationprogram directed to an exemplary installation and service industry. Adriver of a vehicle 4666 enters the premises via a dock. Uponestablishing a link with the network, the terminal 4667 reports itsstatus. In response, the terminal 4667 receives from the computer 4652 acommand via the premises network to load a docking application. Afterdetermining that it does not have the docking application storedlocally, the terminal 4667 transmits a program code request specifyingthe application. Because of previous activity, for example, the accessdevice 4659 (which receives the transmission) happens to have theprogram code stored locally. It fields the request, sending the list ofprogram objects along with the “interpretive” program object sequence.Upon receipt, the terminal 4667 might identify that all program objectexecutable code is stored locally, and, therefore, begins to execute theapplication program. Otherwise, if certain program object executable isnot locally stored, the terminal 4667 transmits a subsequent request.This time, the access device 4659 might not currently store theexecutable program object code. Thus, the access server 4659 routes therequest downstream toward a device which does store the code. Oncelocated, the code is delivered upstream to the terminal 4667 forexecution.

Requested data or program code may reside in one or more of those of theaccess devices 4605, 4607, 4609, 4611, 4613, 4615, 4617, 4619 and 4621which happen to be configured as access servers. Otherwise, the data orcode may be reside in one or more of the computers 4603, 4621, 4623 or4625, if they are configured as servers.

For example, assuming that the access device 4619 has been configured asan access server and happens to store data needed by the terminal 4601,the terminal 4601 would begin the process of retrieving the data byformulating a data request. As previously mentioned, the data requestdoes not identify the access device 4619, but only identifies the neededdata. After formulation, the terminal 4601 routes the request downstreamto the access device 4605. Upon receipt, the access device 4605determines that it does not store the requested data, and fails toidentify the requested data in a routing table entry. Thus, the accessdevice 4605 forwards the data request to the access device 4607. As withdevice 4605, the access device 4607 cannot identify the requested dataand routes the request to the access device 4609. Upon receipt, theaccess device 4609 consults its routing table and identifies an entryfor the requested data. The entry lists the next device in an upstreampath to the data, i.e., the access device 4619 is listed. Thus, theaccess device 4609 forwards the data request upstream to the accessdevice 4619. The access device 4619 responds to the data request by: 1)locating the stored data; 2) formulating a routing request (containingthe data) destined for the requesting device, the terminal 4601; and 3)sending the routing request downstream to the access device 4609. Usingits routing table, the access device 4609 identifies the terminal 4601,and sends the routing request (with attached data) upstream to theaccess device 4607. Likewise, the access device 4607 sends the routingrequest upstream to the access device 4605. Finally, the access device4607 sends the routing request to the destination, the terminal 4601,completing the process. Program code (e.g., program objects) may besimilarly stored, requested and delivered.

Similarly, when remote processing is required, a network deviceformulates a processing request which identifies the specific remoteprocessing needed, yet need not identify a processing destination. Afterformulation, the processing request is transmitted downstream toward anaccess server or computer server capable of performing the requestedprocessing. For example, the access device 4617 fields processingrequests from the computer 4603. After determining that it cannotperform the processing, the access device 4617 consults its spanningtree routing table, yet finds no upstream entry for any network devicecapable of performing the processing. Thus, the access device 4617routes the processing request downstream to the access server 4613.Although the access device 4613 has not been configured for suchprocessing, the access device 4613 does find an entry identifying afirst network device, the access device 4615, in an upstream pathway toa location where such processing is handled. The access device 4613forwards the processing request to the access device 4615 which isconfigured as an access server to handle the processing. Thereafter, therequested processing is carried out by the access device 4615, with anyassociated intercommunication with the computer 4603 needed via the samepathway using routing requests.

Thus, each spanning tree routing table not only includes entries for allupstream network devices, each also includes entries for all upstreamdata, program code and processing resources. Moreover, each such entryonly identifies the next network device through which forwarded requestsare to made in the pathway to the request destination. Each spanningtree table also contains an entry designating a downstream route for usewhen no upstream entry can be located.

In the communication network of the present invention, program code,data and local processing capabilities dynamically migrate through thenetwork to optimize network performance. Specifically, each the accessdevices 4605, 4607, 4609, 4611, 4613, 4615, 4617, 4619 and 4621 areconfigured as access servers. However, a specific data object in highdemand is not initially stored in any of the access devices. Instead,the data object in high demand is originally stored on the computer4623, configured as a server.

Upon encountering a first data request by the terminal 4601 for the dataobject in high demand, each of the intermediate access servers, theaccess devices 4605, 4607 and 4609, fail to identify the data objectwhich results in the sequential forwarding of the data request to thecomputer 4623. However, each of the intermediate access servers recordentries for the data in their routing tables with a downstreamdestination. Thereafter, each time that a network device, such as theterminal 4601, requests the data object, the intermediate access serverswhich receive the request bump up a count stored in the routing tableentry.

To make a determination of whether to migrate the data object or not,upon encountering a data request, each intermediate access serverconsiders the: 1) associated count entry; 2) duration of time over whichthe count entry has accumulated; 3) cost of retrieving the data from thedownstream source; 4) the size of the data object; and 5) its ownresource availability (e.g., remaining storage space).

For example, after receiving a high number of recent requests for thedata object and having a relatively high cost in extracting thedownstream object, the access device 4605 determines that migration of acopy of the data object into its own available storage could improvenetwork performance. Thus, instead of sending the data requestdownstream to the access device 4607, the access device 4605 substitutesand forwards a migration request instead of the data request.

Upon receiving the migration request, the remaining intermediate accessservers, the access devices 4607 and 4609 merely forward the migrationrequest to the computer 4623. In response, the computer 4623 records themigration event, i.e., the data object migrated and the migrationdestination (the access device 4605), for future updating control.

The computer 4623 also forwards a copy of the data object to the accessdevice 4609 for relaying to the access device 4605 via the access device4607. Upon receipt, the access device 4605 stores the data objectlocally, and forwards a further copy back to the requesting networkdevice, the terminal 4601. Thereafter, instead of relaying each datarequest for that data object downstream, the access device 4605 respondsby sending a copy of the locally stored data object toward therequesting device. In other words, the access device 4605 haseffectively intercepted a copy of the data for local storage, and,thereafter, forwards a copy of the locally stored copy to service anyincoming requests.

In addition, upon forwarding the data object from the source, thecomputer 4623, to the destination, the terminal 4601, the data objectsize and link cost associated with reaching a given intermediate accessdevice is recorded. For example, if a wired communication link betweenthe computer 4623 and the access device 4609 is assigned a cost of “1”,after fielding the data request, the computer 4623 constructs a dataresponse which not only includes the requested data object, but alsoincludes a link cost entry of “1” and an indication of the data objectsize. In turn, the access device 4609 identifies the cost to the accessdevice 4607, for example a cost of “3”, the access device adds the “3”to the pending cost entry in the data response, and forwards theresponse to the access device 4607. Similarly, the access device 4607assesses a cost of “3” for the communication link to the access device4605, adds the “3” to the pending cost entry of 114, and forwards thedata response to the access device 4605. After assessing a cost for thelink to the terminal 4601, for example a cost of “4”, the data responseis delivered to the terminal 4601. Thus, the terminal 4601 sees that toaccess the data again, it will most likely result in “11” units ofcommunication cost. Moreover, for example, the terminal 4607 considersthe cost of “3” when determining whether to migrate the data object ornot.

Similarly, when a migration of a data object occurs, all intermediateaccess devices record the cost of the upstream link to the copy of thedata object. Thereafter, upon receiving a data request for the dataobject, an intermediate access device can compare the cost of theupstream pathway to the copy with the downstream pathway to the originaldata object to choose the pathway with the lesser cost. A notificationof deletion of a copy of a data object destined for a downstream sourceis also noted by each intermediate access devices, requiring deletionsof the entries for the “copied then deleted” data object.

For example, if a locally stored copy of the data fails to be used for aperiod of time determined by the access device 4605 to be too long tojustify local storage (in view of the communication link costs back tothe original source, the size of the data object, and potentiallydwindling local resources), the access device 4605 deletes the locallystored copy of the data, and routes to the computer 4623 an indicationthat the local copy of the data object has been deleted. Upon receivingthe indication for relaying, the intermediate access devices 4607 and4609, in turn, remove from their routing tables the entries to therecently deleted upstream copy. Upon receipt of the indication, thecomputer 4623 records the deletion, completing the purging process.

Although data objects were used above to describe the migration process,program code (or program objects) are similarly migrated to and deletedfrom local storage. In addition, to prevent instability, a certainamount of hysteresis must be built in to prevent vacillating migrationand purging decisions.

In assigning cost units to the various communication links, comparisonsbetween factors such as actual monetary costs, bandwidths, delays,loading and power consumption are taken into consideration. Moreover,such costs are stored as sub-entries in the spanning tree routingtables.

Although only migration of a copy from a source to a single destinationwas previously described, if a data or program object proves to be inhigh enough demand, several, or even all, access devices in the networkmight store a copy. All that is required is that each access deviceexperience a significant and sustained quantity of requests for a commondata object (or program code/object) to justify the storage of a localcopy in view of communication link costs and available local resources.

Processing resources are similarly migrated and purged. To service aprocessing request, an access device must be configured not only withsufficient hardware resources but must also store the programming codeand associated data necessary to perform the requested processing.

For example, if the terminal 4601 desires to search prior salesinformation but can neither store the information or the necessarysearch program routines because of limited local resources, the terminal4601 formulates a processing request which it routes downstream to theaccess device 4605. In the illustrated embodiment, the access device4609 is originally configured with the hardware and software necessaryto perform the processing request. In particular, the access device 4609uses bulk storage devices to store past sales data, and executes asearch program in response to received processing requests.

Although the intermediate access server 4607 is configured withappropriate processing and storage resources, originally, it does notstore the search program or the past sales data. Thus, while receivingrepeated processing requests from the terminal 4601 via the intermediateaccess device 4605, the access device 4607 initially logs the request inits routing table and forwards the request downstream to the accessdevice 4609 which fields, processes and responds to the requests.

Because the frequency of the requests, costs and available localresources, when not busy, the access device 4607 sends a migrationinquiry downstream to the access device 4609. Upon receipt, the accessdevice 4609 responds by sending an indication of the volume of thepotential transfer upstream, to the access device 4607. Based on theindication along with the aforementioned other migration factors, theaccess device 4607 may or may not pursue the migration.

If migration is chosen, the access device 4607 assembles a migrationrequest identifying the desired processing, and routes the requestdownstream to the access device 4609. In response, the access device4609, records the migration (for future updating) and begins to transfera copy of the program (or programming object(s)) and the past salesinformation to the access device 4607, preferably occurs during periodsof low network traffic.

Although intermediate access devices between the source and destinationof the processing migration are not shown in the exemplary illustrationabove, any intermediate access devices that do occur follow the sameprocedures previously set forth in reference to data object migration,recording and purging routing table entries to upstream and downstreamprocessing devices.

As may be appreciated in view of the foregoing, in many instances,migration does not always flow immediately to the access device nearesta requesting network device. Instead, for example, an access devicewhich receives the same data or program code requests from a pluralityof different terminals will perform migration before any upstream accessdevice unless upstream link costs are comparatively much higher.

FIG. 46 b is a diagram which further illustrates the migration andpurging process. In particular, a premises network consists of computers4651 and 4652—configured as servers, a wired LAN 4653, and accessdevices 4655, 4657, 4659, 4661 and 4663—configured as access servers. Aportable computer terminal 4664 participates in the premises networkwhich exhibits migration and purging as described above in reference toFIG. 46 a. In addition, a vehicular network is shown which consists of amobile access server 4665 and a portable computer terminal 4667.

As illustrated, each of the access devices 4655 and 4659 are configuredfor long distance, wireless communication with the access server 4665via a second higher power radio and associated antenna, e.g., WAN,paging, cellular, etc. The corresponding first radio and associatedantenna are used for relatively lower power premises networkcommunication.

Because of the much higher cost associated with the communication linkbetween the access server 4665 and the access device 4659, the accessservers 4665 is much more likely to engage in the dynamic migration ofdata/code objects or processing resources than the other access serverslocated within the premises network. With a link cost assessed at “20”for example, the mobile access server 4665 rapidly decides to migrate,while slowly deciding to purge migrated data. The migration/purgingprocess used is the same as that described above in reference to thepremises network of FIG. 46 a.

In addition, because of the high link cost, the mobile access server4665 is also configured to provide anticipatory migration, and respondsto direct migration commands from the terminal 4667 or other controllingnetwork devices. Specifically, anticipatory migration may occur in twoways. First, if a driver is preparing to leave the premises to service aspecific appliance, for example, the schematic diagram of the appliancemay be migrated to the mobile access server 4665 in anticipation offuture use. This form of anticipatory migration may be directed from acontrolling device downstream in the premises network, e.g., thecomputer 4652 which also stores the schematic diagram, from the terminal4667 upstream, or from the access server 4665 itself upon analysis ofthe work order.

A second form of anticipatory migration originates at the access server4665 (although the resulting migration control could originate either upor downstream). The access server 4665 anticipates future migrationneeds through the storage and analysis of previous requests fordata/code objects or processing resources. For example, if the accessserver 4665 determines that nearly every time the terminal 4667 requesta given program code or program object, the terminal 4667 follows thatrequest a short time thereafter with further requests for specific dataobjects. In such circumstances, instead of repeatedly initiating,requesting and delivering portions of data over the communication thehigher cost link, the requested and anticipated requests are all handledin one communication session, saving money and time.

Similarly, the terminal 4667, through program design or through requestmonitoring, can also participate in anticipatory migration. For example,the terminal 4667 can be programmed to make all upcoming requests at onetime, and often in advance of leaving the low power radio range of thepremises network. The terminal 4667 can also be specifically programmedto issue direct migration and purging commands to the access server4665, permitting further control of the migration process and systemresources of the mobile access server 4665. Moreover, the terminal 4667may be configured to historically monitor all requests so as toanticipate subsequent requests in the manner described above inreference to the access server 4665.

In addition, the terminals 4664 and 4667 are configured to receivekeyed, voice and pen input. Other types of input such as video orthumbprint image capture might also be added. The terminals 4664 and4667 can also be configured with code reading/image capturing devices,or be configured to receive input from external code reading/imagecapturing devices (via tethering or low power wireless links). Eachterminal also provides voice and LCD (liquid crystal display) output forthe user. Thus, it can be appreciated that there are many types of datato be delivered to and from the terminals 4664 and 4667. The data maytake on the forms of keyed or penned in command information, pennedimages or signatures, captured images of 2-D codes, signatures, etc. andvoice signals, for example.

Each type of data handled by the terminals 4664 and 4667 places specificrequirements on the communication network. For example, whencommunicating voice signals, a communication channel or link providingreal time voice delivery is often required. Dedicated bandwidth may bereserved for such communications through the spanning tree networkillustrated, or can be established via a cellular link with the accessdevice 4655. Cellular radios may be built into the terminals 4664 and4667 (via PCMCIA slots, for example) or via tethered cellular phones.

If post-processed, signature images require at most a delayed deliveryof a plurality of such images over inexpensive and possibly slower orless convenient communication links. Relatively small packages of oneway communication to the terminal 4667 may travel through a lower costpaging network for delivery. They could also travel through the spanningtree network, cellular networks, or through other higher cost, two wayWANs.

Because programs cannot always anticipate all of the availablecommunication channels through which the different types of data mayflow (availability which not only changes from one network installationto another, but also changes within a given installation due to terminaland device configurations and their locations within the network), therouting tables within each network device subdivide routing informationbased on the type of data to be forwarded.

For example, the access device 4665 begins receives a communication fromthe terminal 4667. The communication takes the form of a requested linkfor voice signal data destined for the computer 4651. In response, theaccess device 4665 consults its routing table, determines that voicedata can take one of two pathways: through either a cellular radio orWAN route to the access device 4655. In response, the access device 4665delivers the communication route options to the terminal 4667 for userand/or software consideration.

If the request is not aborted and the cellular route is selected, theaccess device 4665 establishes a cellular link with the access device4655, and requests a voice link with the computer 4651. In response, theaccess point 4655 consults its routing table, and, for voice data to thecomputer 4651, it identifies the need for dedicated wired bandwidth onthe wired LAN 4653 directly with the computer 4651. In response, theaccess device 4655 places the request on the wired LAN 4653. Inresponse, the computer 4651 communicates an acknowledge message which isrouted through the access device 4655 to the access device 4665. Theaccess device 4665 delivers the acknowledge message to the terminal4667. At that point, the terminal 4667 begins sending the voice data tothe computer 4651 through the designated route.

If the cellular link to the access device 4655 is in use or theend-to-end link otherwise proves unavailable, the access device 4665reports the status, again offering the remaining communication route viathe WAN. If selected, the access device 4665 establishes the pathway tothe access device 4659 via WAN communications. In turn, the pathway isestablished through the access device 4657, access device 4655 and thecomputer 4653. With a returned acknowledge from the computer 4653, theterminal 4667 begins voice communication.

Similarly, communication pathway between any other two network devices,such as from the computer 4651 to the terminal 4664, can be established.For example, if the computer 4651 desires the user of the terminal 4664to obtain and compare a penned signature image for comparison with anauthenticated signature stored at the computer 4651, the computer 4651first attempts to communicate the request and image data to the terminal4664 via the premises network. If the terminal 4664 happens to be out ofrange of the premises network, the computer 4651 attempts to page theterminal 4664 with the comparison request. In response, the terminal4664 considers the data type via its routing table, identifies theroute(s) available, and offers the route options to the user and/orprogram at the terminal 4664. If selected, the terminal 4664 establishesthe selected communication link for the delivery of the associatedcomparison image.

Moreover, because of the high cost associated with the communicationlink from the access device 4665 to the premises network, the accessdevice 4665 stores several types of lower priority data until such timeor data storage size justifies delivery. Such deliver may not occuruntil the vehicle returns to the premises network, e.g., to a dock atthe premises.

In addition, requests for communication may also include specificlimitations. For example, the need for voice data only in real time canbe specified, and will result in no consideration by any intermediatenetwork device of other pseudo-random real time link options. Lowestcost delayed delivery can also be specified corresponding results.Requests with high priority specified, choose the fastest communicationlink regardless of cost.

Moreover, the terminals 4664 and 4667 can be configured to operaterunning application software under the DOS, Windows or OS/2 operatingsystem environments.

Communication between the terminal 4667 and the access device 4665occurs via an infrared link if the terminal 4667 is docked within thevehicle. Routing tables within the access device 4665 and terminal 4667both contain dual entries for communication exchange pathways. First,the infrared link is attempted, if available. Otherwise a lower power RFcommunication transmission is used. Although a wired docking arrangementmight be used instead of infrared, infrared is preferred inside thevehicle for ease of installation and to minimize wire clutter. Suchinfrared installations also provide support for communicating withprinters, scanners and other peripheral devices within the vehicle,i.e., the vehicular LAN preferably operates via infrared except whencommunicating with a remotely located terminal 4667 or with otherremotely located network devices.

In another embodiment illustrated by FIG. 46 b, service personnel usethe vehicle 4666 for visiting customer sites. At the site, the terminal4667 is carried within the customer's premises. Ordinarily,communication with the premises network would take place via relativelylow power radio transmissions between the terminal 4667 and the accessdevice 4665. However, communication can be achieved via a telephone jacklink at the customer site, if: 1) the customer site blocks suchtransmissions; 2) the transmission range is exceeded; or 3) link costsor channel speed so justify. Once plugged into the telephone jack, theterminal 4667 automatically activates inactive routing table entries (bysetting a flag therein) corresponding to possible telephone jack links.Thereafter, communication attempts to either the vehicular or premisesLAN will offer routes via the customer's telephone jack link.

FIG. 47 a is a flow diagram which more specifically illustrates thefunctionality of the access servers of FIGS. 46 a-b in handling data,processing and routing requests. At a block 4701, an access serverawaits incoming communications which take the form of several types ofpreviously mentioned requests such as data, object, processing,migration and routing requests. In addition at the block 4701, theaccess server awaits the need to perform migration evaluation andprocessing, i.e., a time cut period to lapse which occurs once everyfifteen (15) minutes. This period may be modified (lengthened orshortened) as proves necessary depending on channel loading conditions.

Upon receiving a routing request as indicated at the event block 4703,the access server accesses its routing table, at a block 4705, in anattempt to identify the destination of the routing request in anupstream path. If the destination is identified, the access serverforwards the routing request to the next network device in the upstreampath toward the destination, at a block 4707. Otherwise, if thedestination is not identified in the routing table at the block 4705, atthe block 4707 the access server transmits the routing request to thenext network device in the downstream path. Thereafter, the accessserver returns to the block 4701 to await another event.

At the block 4701, upon receiving and logging a migration request, theaccess server vectors from an associated event block 4709 to determinewhether it stores the requested migration information (e.g., therequested code or data or the program code and/or data associated with aprocessing resource migration request) locally or not at a block 4711.If not, the access point branches to the block 4705 to identify theclosest (or any) network device in the spanning tree pathway. Forexample, if the routing table carries no entries for the migrationinformation, the access server routes the migration request to the nextdownstream network device. Otherwise, if the routing table carries onlyan upstream or a downstream entry, the access server routes the requestas specified by the routing table. However, if more than one entryexists for the requested migration information, the access server routesthe migration request along the lowest cost spanning tree pathway (asindicated in the routing table).

However, if, at the block 4711, the access server determines that itstores the migration information locally, the access server: 1)retrieves the migration information and records the migration event forupdate control, at a block 4713; 2) accesses its routing table toidentify the forwarding pathway, at the block 4705; 3) forwards theretrieved migration information, at the block 4707; and 4) returns tothe block 4701 to await another event.

After receiving and logging (counting the occurrence of) a processingrequest at the block 4701, the access server branches via an event block4715 to determine whether the requested processing can be performedlocally or not at a block 4717. If not, the access server forwards theprocessing request at the block 4707 per routing table instruction atthe block 4705. Afterwards, the access server returns to the awaitanother event at the block 4701.

However, if the access server determines that it can perform therequested processing at the block 4717, the access server performs theprocessing at a block 4719, generates a response at a block 4721, routesthe response back to the requesting network device at the block 4707 perrouting table instruction at the block 4705, and, finally, returns tothe block 4701 to await another event.

Upon receiving and logging a data or code request at the block 4701, theaccess server vectors via an event block 4723 to determine whether therequested data or code is stored locally at a block 4725. If so, theaccess server branches to a block 4727 to retrieve the data or code fromstorage. Thereafter, the data or code is forwarded at the block 4707 perrouting table instruction at the block 4705. Once forwarded, the accessserver branches to the block 4701 to await another event.

At the block 4725, if the access server determines that the requesteddata or code is not stored locally, the access server considers whetherit should migrate the data at a block 4729. The access server analyzesthe overall link cost, the size of the requested data or code, thefrequency of such requests, available local storage resources (some ofwhich it may determine to recapture by purging other locally storeddata, code or processing resources) Specifically, if sufficient localresources are (or can be made) available, the access server determinesthe weighted average frequency of the requests for that data or code.The frequency is then multiplied by a predetermined fraction (50%) ofthe overall link cost for retrieving the data or object to the accessserver from the current source. The resulting number is then compared toa migration threshold number, for example “10”.

If, at the block 4729, the access server determines that the thresholdnumber is greater than the resulting number, the access server, decidingnot to migrate, branches to route the data/code request per routingtable instruction at the blocks 4705 and 4707. Alternatively, if theaccess server determines that the threshold number is equal or less thanthe resulting number at the block 4729, the access server decides tomigrate. Thus, at a block 4731, the access server creates and sends amigration request (instead of merely forwarding the data/code request)and awaits delivery of the requested code or data. Upon receipt, at ablock 4733, the access server stores the data or code. Thereafter, thedata/code is retrieved at the block 4727 for routing to the requestingnetwork device via the blocks 4705 and 4707. Once routing is complete,the access server again returns to the block 4701 to await anotherevent.

Finally, upon receiving a time out event signifying the periodic need toperform migration evaluation and processing, the access server branchesto execute migration procedures at a block 4737, as described in moredetail below.

FIG. 47 b is a flow diagram utilized by the access servers of FIGS. 46a-b to manage the migration of data and program code from a sourcestorage and/or processing device toward an end-point device. Morespecifically, the exemplary flow diagram illustrates the migration andpurging procedures represented by the block 4737 of FIG. 47 a.

Upon encountering a time out event (occurring every 15 minutes), anaccess server begins the illustrated procedure of FIG. 47 b. At a block4751, the access server retrieves a data/code entry from its routingtable for which it provides local storage. At a block 4753, the currentcount recorded (indicating the number of requests for that data/codeentry during the current time out interval) is multiplied by two thirds(⅔) and added to one third (⅓) the value of the previously recordedweighted frequency. The access server records the result as the newweighted frequency in the routing table entry. This weighting offrequency constitutes an “aging” of the data/code routing table entry.

At a block 4755, fifty percent (50%) of the overall cost of the link,i.e., from the access server to another source of the locally storeddata/code, is multiplied by the newly recorded weighted frequency. Theaccess server compares the results of the multiplication with ahysteresis threshold at a block 4757. The hysteresis threshold is alsoreferred to herein as a purging threshold. In premises networklocations, for example, the hysteresis threshold is set at five (5)units below the migration threshold of the block 4729 in FIG. 47 a.However, the migration and hysteresis thresholds may need be modified inalternate network embodiments, such as may be found in vehicular networkinstallations.

If the hysteresis threshold is exceeded, the access server determinesthat it should continue to store the data/code, and branches to a block4759 to determine whether there are any remaining entries for locallystored data/code which have not yet been considered for purging.Alternatively, if the hysteresis threshold is not exceeded, the accessserver determines that the data/code item should be purged, and does soat a block 4761. Thereafter, the access server branches to the block4759.

If, at the block 4759, other data/code items which have not yet beenconsidered for purging, the access server repeats the purgingconsideration of the blocks 4751 through 4759 until all locally storeddata/code items have been considered. At that point, the access serverbranches to block 4763 to begin migration and purging consideration ofprocessing resources.

First, the access server retrieves a routing table entry relating toprocessing resources, i.e., supporting program code and any associateddata. At a block 4765, the access server ages the entry, i.e., performsthe aforementioned weighted frequency averaging. Thereafter, fiftypercent (50%) of the overall link cost is multiplied with the newweighted frequency at a block 4767. If the entry indicates local storageof the processing resources at a block 4769, the access server comparesthe results with the hysteresis threshold at a block 4771. If above thehysteresis threshold, the access server continues to store theprocessing resources, branching to consider any remaining processingresource entries at a block 4775. Otherwise, the access server purgesthe stored resources at a block 4773 before considering any remainingentries at the block 4775.

Alternately, if the routing table entry indicates that the processingresources are not stored locally, at a block 4777, the access serverdetermines whether it has been configured with the hardware necessary toperform the processing. If not, the access server branches to the block4775 to consider process other entries. Otherwise, at a block 4779, theaccess server compares the migration threshold with the result, i.e.,50% of the link cost multiplied by the new weighted frequency. If theresult does not exceed the migration threshold, the access serverbranches to the block 4775 to consider other entries. If the resultexceeds the migration threshold, the access server formulates and routesa migration request for the processing resources, awaits the responsivedelivery and stores the resources locally at a block 4781, beforebranching to the block 4775.

At the block 4775, if the access server determines that other processingresource entries have not be considered for purging or migration, itrepeatedly branches back to the block 4763 to carry out theconsideration cycle until complete. Thereafter, the migration/purgingprocedure ends, and the access point returns to the block 4701 of FIG.47 a to await the occurrence of another event.

FIG. 48 is a schematic diagram of the access servers of FIGS. 46 a-billustrating an exemplary circuit layout which supports thefunctionality described in reference to FIGS. 47 a-b. In particular, atypical access server, an access server 4801, is configured withtransceiver circuitry 4803 and associated antenna 4805 for participatingin the premises, peripheral and/or wide area networks. In addition,another transceiver, a transceiver circuit 4807, and associated antenna4809 might be added, for example, to support WAN or cellularcommunications. Although not shown, interface circuitry for otherwireless or wired communication links may be included in the accessserver configuration when needed.

Processing circuitry 4811 provides at least three processing functionsfor the access server by managing or performing: 1) communicationprocessing functionality; 2) migration and purging; and 3) localresource processing wherein incoming communications. Although in mostembodiments, the processing circuitry 4811 comprises a singlemicroprocessor, it may comprise several. Moreover, if the processingcircuitry 4811 is not configured to perform migration and local resourceprocessing, the illustrated access device operates as an access point.

The processing circuitry 4811 utilizes a memory 4813 for short term andlong term bulk storage. The memory 4813 comprises hard drive storage,dynamic RAM (random access memory), flash memory, and ROM (read onlymemory). However, all other types of memory circuits or devices mightalternately be used.

Specific hardware configurations needed to accommodate specializedprocessing requests are represented by a circuit/device block 4815.However, such hardware need not be present to service relatively basicprocessing requests. Additionally, access servers may either be batterypowered although, if the network configuration permits, AC (alternatingcurrent) power is preferred.

FIG. 49 a is a specific exemplary embodiment of an access server in amulti-hop communication network utilized for remote processing of 1-D(one dimensional) or 2-D (two-dimensional) code information. In thisembodiment, a code reader 4901 is used to capture and transmit codeinformation for further processing, including decoding, by a remoteaccess server in a premises LAN. Specifically, a user brings the codereader 4901, which preferably is a CCD (charged coupled device) typereader, into a reading relationship with a 2-D code 4903 located on acontainer 4905. Light reflected from the code 4903 is received by thecode reader 4901 and directed onto the CCD located within the reader to“capture” the code image.

To enable the CCD to operate properly, however, it may first benecessary for the reader to focus the image on the CCD. Such focusingcan, for example, be performed by conventional techniques known in thecamera art. As another example, one or more spotter beams are presentlyused to ensure that the user is holding the reader the proper distancefrom the code to enable the CCD to properly capture the image.

Once captured, the code image may then be digitized within the reader tocreate a digital signal representative of the code image, which is thentransferred, via RF transmissions, to other network devices for furtherprocessing. Alternatively, the reader 4901 may transmit a modulatedanalog signal representative of the code image to other network devicesfor further processing.

In any event, the code reader 4901, an end-point device, forwards thecode image signal downstream in the premises LAN to the first accessserver in the network that has the capability of decoding the signalinto the usable information represented by the code 4903. As discussedabove, any one or all of the access devices 4907-4913 may be an accessserver and contain the digital signal processing circuitry necessary todecode the code image signal. For example, the network may be designedsuch that the access device 4907 is an access server which performsdecoding for all code readers, such as the code reader 4901, being usedin a designated area. If, however, the access device 4907 is merely anaccess point, or is an access server but does not have decodingcapability, then the access device 4907 relays the code image signaldownstream.

More specifically, and as discussed more completely above, the codereader 4901 sends a processing request downstream to the access device4907. If the access device 4907 is an access point, the processingrequest is simply relayed downstream to the access device 4909. If theaccess device 4907 is an access server, it looks up in its table todetermine whether it has the capability to perform the type ofprocessing requested, i.e., decoding. If it does, the access device 4907sends an acknowledge and the code reader 4901 forwards the code imagesignal to the access device 4907 for decoding. Once decoded, theinformation may be re-transmitted to the code reader 4901 for display ona screen (not shown). In addition, or alternatively, the access device4907 may send a good read signal to the code reader 4901 to indicate tothe user that the reading operation has resulted in a valid reading. Thedecoded information may also be transmitted to a host computer 4915 orother network device for further processing.

If the access device 4907 does not find decode capability listed in itstable, it forwards the processing request downstream to access device4909. Likewise, if access device 4909 is an access point or an accessserver without decode capability, the processing request is forwardeddownstream to the access device 4913. Once access device 4913 receivesthe processing request, it also examines its table to determine whetherit, or any device upstream of it (such as, for example, access device4911), has the capability to service the processing request. If it doeslocate such capability, it sends an acknowledge upstream to the codereader 4901 which forwards the code image signal to the access device4913 for decoding thereby or for routing to the upstream access devicehaving that capability.

If the access device 4913 does not locate decode capability in itstable, it forwards the processing request to host computer 4915 fordecoding thereby or so that the host computer 4915 can locate a devicehaving the capability to service the processing request. Of course, asmentioned above, the network could be configured such that each one ofthe access devices 4907-4913 is an access server having the circuitrynecessary for decoding.

While a CCD type code reader is preferred with respect to the embodimentof FIG. 49 a, other types of code readers, including laser scanners, arealso contemplated. Furthermore, while the above description places thedecoding circuitry in a device external to the code reader 4901, thecode reader 4901 may house such decoding circuitry and may transmitdecoded data to external network devices for further processing.However, there are many advantages to placing the decoding circuitryexternal to the code reader 4901. For example, because the code readeris a portable device and likely battery-powered, power conservation aswell as reader size and weight become important design considerations.By placing the decoding circuitry in a device external to the reader4901, the reader uses less power and may be smaller and lighter than ifthe decode circuitry is placed in the code reader 4901. Further, in anenvironment where numerous code readers are used, placing the decodecircuitry in one or a few external devices rather than all readers,which are often dropped by users, reduces the chances that the decodecircuitry will be damaged. In addition, such a configuration reduces theamount of circuitry used and consequently results in lower readermanufacturing costs.

In addition, the code reader 4929 is configured to collect signature,printed text and handwriting images for further processing. Althoughfurther processing can be performed on-board, within the reader 4929, inone embodiment it occurs within an access server.

Either way, such processing first involves the identification of thetype of information contained within the image. If the user does notsimplify the process by identifying the type of image captured,automatic identification is invoked. This occurs by first attempting toidentify the image as a 2-D code. If this fails, the processing involvesan attempt at character recognition to identify any printed text thatmight exist within the image. If no text is found, an analysis isperformed to determine whether the image is a handwritten signature.Finally, if all else fails, the image is generically classified as apicture. Several examples of pictures include: images of bakery shelfspace in a given store for subsequent collection and evaluation of onescompetition; images of broken equipment for transmission to remoteexperts for service advice; and images of meter displays for billingverification.

After identification, each type of data receives yet further processing.Decoded 2-D code information is forwarded and acknowledged. Handwrittensignatures are compared with known authentic counterparts. Other typesof S images may be associatively forwarded, stored, displayed and/oracknowledged.

FIG. 49 b is an alternate embodiment of FIG. 49 a wherein communicationbetween the 2-D code reader and the access devices takes the form ofmodulated infrared transmissions. Specifically, as discussed above withrespect to FIG. 49 a, a user uses a code reader 4917 to read a 2-D code4919 on a container 4921. The user then points the code reader 4917 atan infrared transceiver 4923 of an access device 4925 and transmits aprocessing request to the access device 4925 using infraredtransmissions. To facilitate receipt of the infrared transmissions bythe infrared transceiver 4923, the reader may disperse itstransmissions, say, for example, four inches over a distance of tenfeet. Such dispersion allows a user to be less accurate in aiming thecode reader 4917 at the infrared transceiver 4923. The infraredtransceiver 4923 may be, for example, a phototransistor/photodiode pair.

As above, if the access device 4925 is simply an access point, theprocessing request is simply relayed downstream, via either RF orinfrared transmissions, to a further access device downstream. If theaccess device 4925 is an access server, it looks up in its table todetermine whether it has the capability to perform the type ofprocessing requested. If it does, the access device 4925 sends anacknowledge via infrared transmissions to the code reader 4917 and thecode reader 4917 forwards the code image signal to the access device4925 via infrared transmissions for decoding. The access device 4925 maythen transmit the decoded information to the code reader 4917 fordisplay on a screen and/or forward the decoded information to a hostcomputer 4927 for further processing.

If the access device 4925 does not find decode capability listed in itstable, the access device 4925 forwards the processing request to one ofthe access devices 4924, 4926, or 4928 to locate such decodingcapability similarly as discussed above with respect to FIG. 49 a. Whensuch a device is located, the code reader, via infrared transmissions,performs a batch forwarding of the stored image data to the accessdevice 4925 for eventual decoding by one of the access devices 4924,4926, or 4928 or by a host computer 4927 or another device in thepremises LAN (i.e., whichever is the first device located that has thedecoding capability). In this embodiment, communication between accessdevices may be achieved using either RF or infrared transmissions.Furthermore, a user may choose to directly communicate with any specificaccess device in the network simply by pointing the code reader 4917 atthat device and transmitting a processing request.

FIG. 49 c is an alternate embodiment of FIG. 49 a wherein indirectcommunication between the 2-D code reader and the access servers takesplace via holstering or docking access servers. Specifically, asdiscussed above with respect to FIG. 49 a, a user uses a code reader4929 to read a 2-D code on a container. The user then places the reader4929 in a holster access device 4931. The user may support the holsteraccess device 4931 by a shoulder strap 4933 and belt 4935 to facilitateportability.

In one embodiment, the holster access device 4931 may be configured toperform decoding so that when the code reader 4929 is placed inside theholster access device 4931, the code reader 4929 may transmit the codeimage data to the holster access device 4931 for immediate decodingthereby. Alternatively, if the holster access device 4931 does not housethe necessary decoding circuitry, the holster access device 4931transmits a processing request downstream to one of access devices4937-4943 to locate such decoding capability similarly as discussedabove with respect to FIG. 49 a.

In a scenario where numerous codes 4945 are to be read successively bythe code reader 4929, the code reader 4929 may store the read image dataand perform a batch transmission to the holster access device 4931 forimmediate decoding thereby if the holster access device 4931 isconfigured with decoding circuitry. In another embodiment where theholster access device 4931 is not so configured, the code reader 4929transmits a processing request to the holster access device 4931 viainfrared transmissions. The holster access device 4931 in turn forwardsthe processing request downstream via RF transmission to one of theaccess devices 4937-4943 to locate such decoding capability similarly asdiscussed above with respect to FIG. 49 a. When such a device islocated, the code reader, via the holster access device 4931, performs abatch forwarding of the read image data for eventual decoding by one ofthe access devices 4937-4943 or by a host computer 4947 or anotherdevice in the premises LAN (i.e., whichever is the first device locatedthat has the capability).

In an alternate embodiment, batch transmission of stored image data maybe performed via a docking access server 4949. When a user has completedhis code reading tasks, he docks the code reader 4929 in a bay 4951 ofthe docking access server 4949. Other users, when their tasks arecompleted, may similarly dock their code readers in other bays of thedocking access server 4949. In one embodiment, similarly as discussedabove with respect to the holster access device 4931, once a code readeris docked in the docking access server 4949, the code reader performs abatch transmission of its stored code image data to the docking accessserver 4949 for immediate decoding thereby if the docking access server4949 is configured with decoding circuitry. In another embodiment wherethe docking access server 4949 is not so configured, the code reader4929 transmits a processing request to the docking access server 4949via infrared transmissions. The docking access server 4949 in turnforwards the processing request downstream via RF transmission to one ofthe access devices 4937-4943 to locate such decoding capabilitysimilarly as discussed above with respect to FIG. 49 a. When such adevice is located, the code reader, via the docking access server 4949,performs a batch forwarding of the stored image data for eventualdecoding by one of the access devices 4937-4943 or by a host computer4947 or another device in the premises LAN (i.e., whichever is the firstdevice located that has the decoding capability).

In the embodiments of FIG. 49 b or 49 c wherein a number of codes areread and the captured image data is stored within the code reader forbatch transmission at a later time, it may be desirable to configure thenetwork such that decoding is performed first within the code reader.Specifically, when a user successively reads a plurality of codes, auser can ensure that each reading operation is successful or valid whenthe decoding is done immediately within the reader and the user isprovided some sort of good read acknowledgement by the reader. On theother hand, if the image data is simply stored for later decoding by anoff-site device, the user cannot be sure that each reading operationresulted in a valid read. Such a situation may not be a problem,however, if the code and reader are highly reliable or if simpleinformation, such as a signature, is being read which may not require avalidity determination.

FIG. 50 is a schematic diagram similar to that shown in FIG. 48 whichillustrates the circuit layout used in an access server of FIG. 49 toprocess the 2-D code information. Specifically, in an access point 5001,a processing circuitry 5003 manages 2-D code processing functionality asindicated by a block 5005. Although migration processing functionalityis also present, in some embodiments such as those which use a singleaccess server, the migration processing need not be present.

In a memory 5007, the access point 5001 also stores a database of known2-D images in an image database 5009. To further support 2-D codeprocessing, digital signal processing circuitry 5011 has been added.

As configured, the signal processing circuitry 5011 assists the exactdecoding of 2-D images, and may also be used in the image comparisonprocess of received 2-D images with the database 5009 of stored images.

FIGS. 51 a-b are flow diagrams illustrating the operation of the 2-Dcode processing access servers of FIGS. 49-50. In FIG. 51 a, when theaccess server receives image data via its LAN transceiver, it firstattempts at a block 5101 to exactly identify the code information fromthe received code image data. Specifically, the access server uses itscode processing circuitry to perform an analysis of the received imagedata using a decoding algorithm specifically designed for decoding thetype of code which was read. A number of 2-D code types exist,including, for example PDF-417, Maxicode, etc., which have specificcorresponding decoding algorithms or rules.

After its analysis is complete, the access server next determineswhether the exact identification was successful at a block 5103.Determining whether an identification was successful often depends onthe type of code used. If enough redundancy is built into the code, thenthe loss of a number of bits of data resulting from, for example, apartially blurred image may not be fatal to a successful exactidentification. If, on the other hand, the type of 2-D code being readis less “tolerant,” then even the loss of a single bit might result in afailed exact identification.

In any event, if the exact identification is successful, at a block5105, the access server sends the identified code information to apredetermined destination for further processing, and acknowledges thesuccessful identification. If the exact identification is notsuccessful, however, the access point performs a further analysis of theimage data to attempt to identify the corresponding code information.

At blocks 5107 and 5109, the access server compares the received imageto stored images located in its image database and attempts to locatethe closest or best match. Although grey scale considerations andimage-shifting correlation techniques are contemplated, in a relativelysimple embodiment, such a comparison involve a process of scaling thereceived image to correspond to the stored images, then performing an“exclusive OR” of the received image with the stored images. More exactmatches will yield an overall sum value nearer to zero.

After the access point completes its comparison and has identified theclosest or best match between the received image data and the storedimages, the access point then determines at a block 5111 if the overallvalue resulting from the best match comparison is above a predeterminedaccuracy threshold. Such an accuracy threshold may vary depending on,again, the type of code that was read, and the level of importanceassociated with a good read. If the overall value is below thepredetermined threshold, the access server, as above, sends theidentified code information (corresponding to the best match storedimage) at a block 5105 to a predetermined destination for furtherprocessing, and acknowledges the successful decode.

If the overall value of the best match comparison is above thepredetermined threshold, then, at a block 5113, the access serverforwards a bad read or retry message to the code reader to indicate tothe user to re-read the code.

FIG. 51 b is similar to FIG. 51 a except that the comparison of thereceived image with stored images is performed before any exactidentification is attempted. Specifically, the access server firstcompares the received image to the stored images at a block 5115,identifies the closest match at a block 5117, and determines whether theoverall value of the comparison is above a predetermined accuracythreshold at a block 5119. If the overall value is below the threshold,the code information relating to the best match stored image is simplyforwarded at a block 5121 to a pre-determined destination for furtherprocessing.

If the overall value is below the threshold, then the access serverattempts the exact identification and determines success at blocks 5123and 5125. If such exact identification is successful, then the accessdevice forwards the code information at block 5121. If it is notsuccessful, the access device forwards a retry message to the codereader at block 5127.

FIG. 52 illustrates the structuring of 2-D code information so as tosupport a hierarchical recognition strategy as used by the access serverof FIGS. 49-50. In the image database of an access server, each knownimage are stored and hierarchically organized in sections. Each sectionof image contains information relating to a specific category ofinformation. For example, as shown, images may include a main categoryfollowed by further and further sub-categories. Thus, the image databasestores all of the images in the main or first category at a top level inthe hierarchy. Under each main category image, the image database storesonly those sub-category images which coexist with the main categoryimage on known complete 2-D code images. Similarly, under eachsub-category image, the image database only stores sub-sub-categoryimages which coexist with the main category image and the sub-categoryimage.

FIG. 53 is a diagram illustrating an exemplary 2-D code 5301 wherein thehierarchical structure of FIG. 52 is implemented. From left to right,top to bottom, the illustrated 2-D code provides image portions ofcategories separated by five bit line borders, such as a border 5303. Asshown, the main category image represents “grocery”. The sub-categoryrepresents “beans”, and so on for the further sub-categories.

Using such a hierarchical categorization, the access server can morerapidly perform the process of image comparisons. For example, at a maincategory level in the hierarchy, a grocery image, an office supply imageand general merchandize image might be the only three types of maincategory images known to the access point. If after comparing thereceived and the stored main categorization images, no acceptable matchis found, the attempted comparison ends without ever having to comparethe remainder of the potentially thousands of remaining images stored inthe image database. Similarly, if a main level match is found with thestored office supply image, no comparison need be made with the plethoraof remaining images under the grocery image main category.

Further detail of the efficiency of such a hierarchical organization canbe found below in reference to FIG. 54. In addition, although the 2-Dcode illustrated in FIG. 53 is not necessarily a current 2-D codestandard, the principle of hierarchical organization can be utilized incurrent 2-D code standards to take advantage of the image comparisonefficiencies involved.

FIG. 54 is a flow diagram illustrating the functionality of the accessserver of FIGS. 49-50 in carrying out the hierarchical recognitionstrategy of FIGS. 52 and 53. The access server begins the hierarchicalimage comparison process, and, at a block 5401, extracts from thereceived 2-D image a first subcategory image portion, i.e., the maincategory image indicating “grocery” for example. At a block 5403, theaccess server compares the extracted image with each of the maincategory images stored in the image database. If the closest comparisonfails to fall within an accuracy threshold at a block 5405, the accessserver indicates that the comparison has failed at a block 5407, andends the process.

Otherwise, if the comparison is within the accuracy threshold at theblock 5405, the comparison process continues with the access serverchecking to see if there are any further sub-categories at a block 5409.Because other sub-categories exist, the access point branches to repeatthe process beginning at the block 5401. This time, the access serverextracts from the received image the image portion relating to the firstsub-category (beans) for comparison at the block 5403 with only thosefirst known sub-category images having “grocery” as the main category.

Again if no match within the threshold is found, the access pointvectors to indicate failure at the block 5407, and terminates theprocess. However, if a sub-category match is found, the access pointbranches to handle the sub-sub-category in a similar way. If, at theblock 5409 after successfully repeating the comparison a number oftimes, the access point concludes that there are no furthersub-categories to compare, the access point delivers the 2-D codeinformation stored in the image database and associated with thematching stored image, and successfully ends the code identificationprocess.

The known image database is supplemented by exact decoding asillustrated for example in FIG. 51 b, wherein any successful exactdecode is used to provide both categorized image and informationportions for subsequent decoding through comparison. In addition,although the hierarchical structuring described herein offers manyadvantages, it need not be implemented to carry out the comparisonprocess.

Moreover, it will be apparent to one skilled in the art having read theforegoing that various modifications and variations of thiscommunication system according to the present invention are possible andis intended to include all those which are covered by the appendedclaims.

1. A method of determining data rate in a direct sequence spreadspectrum system, the method comprising: receiving a signal that wastransmitted at a particular data rate, wherein the particular data rateis unknown to a receiver, wherein the particular data rate is one of ahigh data rate or a low data rate, and wherein the high data rate is abinary multiple of the low data rate; processing the signal according toa first data rate, thereby generating a signal corresponding to asequence of bits; and determining the particular data rate according tothe sequence of bits.
 2. The method of claim 1, wherein the methodcomprises initiating proper decoding mechanisms for the particular datarate.
 3. The method of claim 1, wherein the particular data rate isdetermined according to a count of 0's and a count of 1's in thesequence of bits.
 4. The method of claim 1, wherein the particular datarate is determined according to an occurrence of repetition in thesequence of bits.
 5. The method of claim 1, wherein at least one datarate in the plurality of data rates is a binary multiple of an otherdata rate in the plurality of data rates.
 6. The method of claim 1,wherein the particular data rate is selected according to a quality ofcommunication on a communication channel.
 7. The method of claim 1,wherein the transmission times of two different rate signals are thesame duration.
 8. A system for determining data rate in a directsequence spread spectrum system, the system comprising: one or morecircuits for receiving a signal that was transmitted at a particulardata rate, wherein the particular data rate is unknown when received,wherein the particular data rate is one of a high data rate or a lowdata rate, and wherein the high data rate is a binary multiple of thelow data rate; wherein the one or more circuits process the signalaccording to a first data rate, thereby generating a signalcorresponding to a sequence of bits; and wherein the one or morecircuits determine the particular data rate according to the sequence ofbits.
 9. The system of claim 8, wherein the one or more circuitsinitiate proper decoding mechanisms for the particular data rate. 10.The system of claim 8, wherein the particular data rate is determinedaccording to a count of 0's and a count of 1's in the sequence of bits.11. The system of claim 8, wherein the particular data rate isdetermined according to an occurrence of repetition in the sequence ofbits.
 12. The system of claim 8, wherein at least one data rate in theplurality of data rates is a binary multiple of an other data rate inthe plurality of data rates.
 13. The system of claim 8, wherein theparticular data rate is selected according to a quality of communicationon a communication channel.
 14. The system of claim 8, wherein thetransmission times of two different rate signals are the same duration.15. A system for determining data rate in a direct sequence spreadspectrum system, the system comprising: at least one processor forreceiving a signal that was transmitted at a particular data rate,wherein the particular data rate is unknown when received, wherein theparticular data rate is one of a high data rate or a low data rate, andwherein the high data rate is a binary multiple of the low data rate;wherein the at least one processor processes the signal according to afirst data rate, thereby generating a signal corresponding to a sequenceof bits; and wherein the at least one processor determines theparticular data rate according to the sequence of bits.
 16. The systemof claim 15, wherein the at least one processor initiates properdecoding mechanisms for the particular data rate.
 17. The system ofclaim 15, wherein the particular data rate is determined according to acount of 0's and a count of 1's in the sequence of bits.
 18. The systemof claim 15, wherein the particular data rate is determined according toan occurrence of repetition in the sequence of bits.
 19. The system ofclaim 15, wherein at least one data rate in the plurality of data ratesis a binary multiple of an other data rate in the plurality of datarates.
 20. The system of claim 15, wherein the particular data rate isselected according to a quality of communication on a communicationchannel.
 21. The system of claim 15, wherein the transmission times oftwo different rate signals are the same duration.
 22. A method ofdetermining data rate in a communication system, the method comprising:receiving a direct sequence spread spectrum signal that was transmittedat a particular data rate, wherein the particular data rate is unknownto a receiver, wherein the particular data rate is one of a high datarate and a low data rate, and wherein the high data rate is a binarymultiple of the low data rate; processing the direct sequence spreadspectrum signal according to the high data rate, thereby generating adespread signal corresponding to a sequence of bits; determining theparticular data rate according to an occurrence of repetition in thesequence of bits; and initiating proper decoding mechanisms for theparticular data rate.
 23. The method of claim 22, wherein the particulardata rate is selected according to a quality of communication on acommunication channel.
 24. A system for determining data rate in acommunication system, the system comprising: one or more circuits forreceiving a direct sequence spread spectrum signal that was transmittedat a particular data rate, wherein the particular data rate is unknownto a receiver, wherein the particular data rate is one of a high datarate and a low data rate, and wherein the high data rate is a binarymultiple of the low data rate; said one or more circuits for processingthe direct sequence spread spectrum signal according to the high datarate, thereby generating a despread signal corresponding to a sequenceof bits; said one or more circuits for determining the particular datarate according to an occurrence of repetition in the sequence of bits;and said one or more circuits for initiating proper decoding mechanismsfor the particular data rate.
 25. The system of claim 24, wherein theparticular data rate is selected according to a quality of communicationon a communication channel.